Mechanische Rechner der Fliegerabwehr, frühe Lösungen: Flugzeugvermessung im 1. Weltkrieg und danach, ca. 1915–1936

Complete English translation of the original German-language document (34 pages).

Mechanical Computers of Anti-Aircraft Artillery, Early Solutions: Aircraft Measurement in World War I and After, ca. 1915–1936

Overview of This Work

In Germany, several attempts were already made during World War I to estimate the point of intersection between a projectile and an aircraft using various auxiliary devices and “command discs” (Kommandoscheiben). When must the guns be fired, how must the time fuze of the shells be set, and how must the gun sight be aligned? Auxiliary curves, nomograms, and families of curves were used, but scarcely any proper computing devices. These were readings rather than actual calculations. Development was in constant flux — new forms of “command discs” were continually appearing.

Topics covered in this work:

Auswanderungsmesser 1917 (Displacement Meter 1917) — from p. 5
Associated command disc (form of 1921 or later) — p. 8
Patented idea from Sweden, 1917 — p. 12
Mechanical displacement computer, 1917 — p. 15
Trials in Switzerland, 7.5 cm Krupp gun on a turntable, 1917–19 — p. 17
Chronology of found designs, incl. Schönian 1919 — Appendix 1, p. 22
Strange coordinate system — Appendix 2, p. 26
Period impressions (Switzerland) — Appendix 3, p. 29
Sources — p. 32

The targets in the air consisted of observation balloons or relatively slow aircraft, biplanes, etc. Zeppelins were recognized as unsuitable in 1916; aircraft could hit them easily thanks to their size and slow speed — and the slightest hit would let the hydrogen escape. Aircraft were at the beginning of the First World War employed more for observation tasks, and less for combat missions; “aviator arrows” were dropped over enemy ground troops — sharpened thin steel darts approximately 10 cm in length — or also small bombs. The aircraft appear slow and unsteady, and were often biplanes.

Vocabulary:

In Germany the term Entfernungsmesser (range finder) was common; in Switzerland Telemeter was more usual. In Germany the terms Auswanderung and Auswanderungsmesser were used: displacement of the aircraft in apparent angle as seen from the guns, within the projectile flight time. In Switzerland the word Vorhalt (lead) is more common, or Vorhaltewinkel (lead angle), Vorhaltestrecke (lead distance). The displacement can be stated as two numbers, horizontal and vertical (depending on the gun sight), or as a single number in the oblique plane defined by the flight path and the gun position (e.g., in Switzerland: 34 mm Flabkanone 38). In Germany the pair “horizontal and vertical displacement,” or also “horizontal and distance,” was more widespread.

Most devices in World War I referred to direct gun laying: the gunners tracked the aircraft with their aiming optic and kept it continuously in the crosshairs. In addition, between the aiming optic and the gun, the “displacement” (Auswanderung) of the aircraft was set as a variable angle — meaning the sight was mounted so that it could move on the gun. In addition to the displacement, the correction for the curvature of the projectile trajectory was also entered at the sight.

In indirect laying in World War II, the computer calculated the finished angles (azimuth and elevation) at which the gun was to fire, plus the required fuze time. The gunners set the angles delivered by the computer and no longer tracked the aircraft in their own telescope.

Lagewinkel: Vertical angle between the horizon and the aircraft or impact point. Elevation: Steepness of the gun barrel. Schusswinkel, Aufsatzwinkel (firing angle, quadrant elevation): Difference between the barrel axis and the line of sight (due to the curvature of the projectile trajectory).

Author: André Masson, Langenthal

October 2017

Shooting at Aircraft in WWI Germany: The Measurement System

Shooting at an aircraft in WWI in Germany was based on the following measurements:

Entfernungsmesser (Range Finder) Stereoscopic sighting of the aircraft, with 1 m to 4 m measurement base. This remained until the Second World War and was only replaced by radar distance measurements.

Höhenmesser (Altimeter) Graphical reading of flight altitude from slant distance and elevation angle.

Stopuhr, Flakuhr (Stopwatch, Flak Watch) Measures projectile flight time as a function of flight altitude and slant distance; no numerical reading.

Auswanderungsmesser (Displacement Meter) Optical measuring instrument; measures the displacement of the aircraft during the projectile flight time, i.e., from the moment the gun is fired to the point of impact.

Kommandotafel (Command Panel) Provides, at the latest possible moment, a better projectile flight time (in many variants, sometimes also called Kommando-Schieber).

Initial Acquisition of the Aircraft

The following procedure likely applied to most of the numerous designs in existence at the time of the First World War:

First the aircraft is acquired and measured by the telemetry device. With an “altimeter” or “pendulum altimeter” at the end of the telemetry tube (see immediately below), after this first measurement the slant distance, the map distance, the flight altitude, and the elevation angle to the aircraft are already known. Unknown remain the speed and the aircraft course. The necessary values are passed on by shouted commands: from the telemeter to the altimeter standing next to it, from the altimeter to the displacement meter and the command disc (or command panel), and from there to the guns. Near the altimeter and the displacement meter stands the man with the stopwatch, who shouts his “STOP” to the displacement meter operator.

There must have been considerable discipline and care in the shouted commands, so that all participants received their values correctly, unambiguously, and on time. How any of this still functioned in the noise of battle is a question. The measured values cannot really be transmitted continuously by shouting. Telephone wires were also already used instead of shouting.

The telemeter is a long tube, mounted horizontally and pivotably on a tripod, with an optic at each end. The aircraft is sighted from both ends, and by means of coincidence or superimposition methods, or also with a stereoscopic impression and a comparison scale (in binocular vision), the distance to the aircraft is estimated. At the time of the First World War, tubes of 2 m and also up to 4 m were in use. In World War II, 3 meters (Switzerland) or 4 m (Germany) were standard — but 8 m and 10 m tubes were also manufactured, and up to 15 m on ships. The longer the tube, the more cumbersome it becomes for rapid traversing. The author of these lines personally encountered, for the light and medium anti-aircraft artillery in the 1960s, light 1.25 m tubes that were carried directly on shoulder frames to increase speed and agility (tripod only for setting down and resting). Only with the advent of radar did distance measurement with the telemeter entirely disappear.

Principle of the Altimeter: At the end of the range finder (telemeter tube) hangs a freely swinging pendulum. Example: Aircraft stands just over 30° above the mathematical horizon; the man at the range finder calls out “60” hm, i.e., 6 km slant distance. The aircraft has an altitude h of approximately 3 km and a map distance k of 5 km: pass it on!

In practice: The coordinate lines are not at right angles to each other; readings are taken at the right and left edges of the hanging part. The protective cover is cut away at the bottom. Diameter, roughly estimated depending on the tube, approximately 10 cm (in WWII partly considerably larger). Both images from Ref. 4, p. 5 and p. 17 respectively.

Apparently the direct, stereoscopic three-dimensional impression can be read more quickly than adjusting and tracking with inverted-image instruments, where two images must overlap or face each other. In anti-aircraft work, the speed of the measurement process is of central importance. The training and reliability of the telemetry personnel were extremely important. Not everyone was suited to direct stereoscopic assessment of distance; personnel had to be carefully selected.

Pendulum Altimeter

When tracking the aircraft, the telemetry operator automatically sets the elevation angle to the aircraft by rotating the tube about its long axis. At the end of the telemetry tube hangs a small pendulum vertically downward, by means of which — as soon as the slant distance is called out — the flight altitude and map distance can be read off automatically, and the elevation angle can also immediately be passed on numerically. If needed, four measured values would thus have to be passed from the telemeter to the command disc and possibly also to the displacement meter. The pendulum will not hang quietly during lateral or unsteady movement of the tube, but will swing.

Flak Watch for Determining Flight Time

If the slant distance and the flight altitude are known, the projectile flight time is determined and can be read from the corresponding ballistic tables. Since it is not practical to leaf through tables or large sheets of paper, another solution was found with the Flak watch: a kind of hand stopwatch on which the flight time can simply be determined (without reading a number). It has only a single hand that goes around in 12 or 18 seconds. Curved lines are printed on the dial, each line corresponding to a particular slant distance. The watch indicates: projectile flight time as a function of flight altitude for the chosen slant distance determined from the telemeter. The deceleration of the projectile due to air resistance is taken into account.

The watch operator sets the measured flight altitude with a kind of iris diaphragm, similar to a camera: the lower the aircraft flies, the more the circular diaphragm closes. From “Start” to “Stop,” the displacement can be measured — “Stop” is when the hand at the outer edge of the narrowed iris diaphragm intersects the chosen slant-distance line.

Watch on the left: Submitted by Carl Zeiss to the Imperial Patent Office; accompanying letter, June 1916: These are probably fantasy variables, possibly for camouflage? Curved curves: “aircraft speed” 5 … 40 m/s, iris diaphragm with flight altitude 0 … 50 hm. No distance is used; that makes no sense for anti-aircraft work. The variables are named “as an example” in the letter. 5 m/s = 18 km/h!

Watch on the right: Flak 8.8 cm, combat charge v₀ = 790 m/s, possibly 1/3 projectile flight time. Inscribed curves on the dial interpreted as 20 to 105 hm or 2 to 10.5 km slant distance. Iris diaphragm: flight altitude up to 7 km. Both images from Konrad Knirim, www.knirim.de; letter text 1916: http://www.vintagetime.de/index.php/Thread/5112-Carl-Zeiss-Jena-Stopuhr/

The adjustable iris diaphragm is clearly visible. The speeds 5 … 40 m/s are strangely small (values estimated). Time is measured from Start until the outermost visible point of the selected curve. The time cannot be read as a numerical value. Normal Flak watch on the right: Curved curves each correspond to one slant distance.

Correct Flak watch: The smaller the flight altitude, the more strongly the iris diaphragm is closed. In the curvature of the curve lines on the dial, the deceleration of the projectile due to air resistance will be accounted for.

The precision of the “Start” … “Stop” shouted commands will not have been very great — the many cross-calls between team members see to that. At short projectile flight times, the Start-Stop errors will allow only very inaccurate measurements at the displacement meter.

The watch operator stands directly next to the displacement meter, as can be seen from old photographs. The displacement meter measures by how much the aircraft moves laterally and in altitude within the projectile flight time (angular values). Measurement times of one third of the projectile flight time were customary. The displacement is then automatically multiplied by three again. The measured angular lead then goes to the command panel, where a better projectile flight time is read out, as well as the necessary ballistic elevations of the barrels (curvature of the projectile trajectories).

The projectile flight time determined early by stopwatch and the measured displacement are NOT valid from the moment of firing to the point of impact, but from an earlier time! From one source: after the displacement measurement, exactly ten seconds are to elapse for setting the gun sight, for fuzing the time fuze, for loading the gun — then it is fired. In these ten seconds, a better projectile flight time must also be found at the command disc in order to set the fuze — but the point of impact is not yet known in order to set the final lead angles at the guns. Simply setting the previously found displacement values unchanged at the guns for a later time is not correct: the displacement values are time-dependent, i.e., they change continuously, as does the projectile flight time. The later computers of WWII calculated more clearly in mathematical terms; the impact-point prediction was continuously up to date.

Then, however, the contemporary witness, General of Anti-Aircraft Artillery (ret.) Otto von Renz (Ref. 2, p. 51), quotes — probably referring to a time before the Auswanderungsmesser 17 or even before the AM15:

“Such command panels were drawn up for various target altitudes … up to 2500 m, for distances graduated … up to 5000 m, and for target speeds of 10, 20, 30, 40 m/s. Their primary purpose was to serve for learning, through drill, how to make free estimates of the lead values and convert them into firing commands. During actual shooting, the panels could not be used because they could not be utilized in the short time available to the shooter.”

The speeds given here correspond exactly to those of the watch (on the left) illustrated above! What was flying so slowly? Were those still balloons, Zeppelins? 10 m/s = 36 km/h, 30 m/s = 108 km/h.

Ref. 2, p. 52: “The instruments were continuously improved; almost every year an improved instrument appeared.” On the new command disc of 1916: “Only reluctantly were the old anti-aircraft artillerists prepared to accept it, but it did produce better results.”

The Auswanderungsmesser 17 (Displacement Meter 1917)

Overall view, approximately 30 cm long, at head height for viewing into the eyepiece: Bell-shaped, fixed — a spiral, displaceable pattern — mounted on a tripod. The observer looks from the left through the eyepiece; the one handwheel visible at the front left adjusts the elevation angle, and is defective in the photo. To the right, looking obliquely upward toward the aircraft, the vertical direction of the viewing angle is adjustable via handwheel. The device remains horizontal at all times.

The spiral pattern is displaceable. Lines curved horizontally: in the AM 17, these lines curve differently “depending on the set elevation angle.”

Image: www.fernglasmuseum.at, more precise address see below.

Leftmost image (both lines belong to the address!): https://www.flickr.com/photos/81567686@N00/sets/72157621767350301/

Photo also at: https://www.flickr.com/photos/dirk_bruin_vlieland/3734912626/in/photostream/

Purpose and Function of the Auswanderungsmesser 17

The purpose is clear, the form of the line grid not yet. The displacement meter must measure the angle by which the aircraft shifts in the sky — as seen by the observer — within the projectile flight time. The standard practice was to run the measurement over one third of the (already early determined) projectile flight time and to read off results that have already been multiplied by three.

Eyepiece image from Ref. 1, p. 14: The bell-shaped curves stand fixed in the eyepiece; from 1917 the second pattern is displaceable “corresponding to the terrain angle,” and appears to adapt the curvature of the curves to the chosen terrain angle (= elevation angle). The pattern suggests that the displacement is indicated as a pair of numbers: lead in azimuth / in altitude.

If the displacement angle were read as a single number, measured in the obliquely oriented plane of the flight path, then parallel, adjustable lines would need to be fitted to the apparent flight direction. However, that requires a second adjustment knob. The aircraft can fly in all possible apparent directions given a fixed terrain angle (= elevation angle). With two separate adjustments, the elevation angle to the aircraft and the inclination of the trajectory curve would need to be set separately — this is not present on the device.

How the two displacement angles are read from this line pattern requires explanation: mysteries are still concealed within this.

The anti-aircraft position is at the center of the sphere; azimuth (geographic longitude) and elevation angle (geographic latitude) are used as coordinates. A horizontal fly-past sweeps through more azimuth in a given time when the elevation angle is greater (in a direct overflight there is a jump of 180° in the shortest time). It is hopeless to correctly estimate the azimuth lead with a fixed azimuth grid in the field of view (bell curves, above), because the spacings in azimuth must depend on the elevation angle. The field of view in the eyepiece is 8.4° in elevation and azimuth (production after Feb. 1941), i.e., about as wide as the spacing of the 10° meridians at 33° latitude. The narrowing of the azimuth lines visible in the eyepiece only occurs over incomparably larger ranges of elevation angle.

In the eyepiece image of the AM 17, the intervals of the azimuth angle narrow by approximately a factor of 1.5 per 4° higher toward the zenith, as read from the image (elevation angle estimated from the field of view). Mathematically, the coordinate grid would require:

Factor of 1.03 per 4° (if the aircraft stands 20° altitude above the horizon)
Factor of 1.07 per 4° (if the aircraft stands 45° altitude above the horizon)
Factor of 1.21 per 4° (if the aircraft stands 70° altitude above the horizon)

So it clearly cannot work in this direct manner. A further attempt at interpreting the bell curves: if the aircraft stands low on the horizon, the displacement must be determined at the very bottom of the field of view — if it stands very high, the displacement is to be measured at the very top of the field of view.

The marked increase in the width of one degree (or other unit) at the very bottom of the field of view, where nothing should be changing, does not fit at all with such an emergency interpretation… actually nothing is understood here. This is written in small text so that as few people as possible will notice: something else in the geometry does not add up either!

Very little is known — it is perhaps possible that these late-produced displacement meters (see the following text) were not made for air defense at all, but for other purposes (possibly anti-tank) ??

More comprehensible than the bell curve, however, is the (depending on the elevation angle) variably shaped curvature of the lines of constant elevation angle — i.e., the parallels of latitude in the globe model. This is documented by the following photo below left: Straight wooden beams in a vertical wall = flight paths for straight-and-level flight. Light horizontal circular arc = circular flight around the observer, everywhere with a fixed elevation angle: that is the only flight in which the elevation-angle coordinate remains fixed. The curvature of the lines “fixed elevation angle” in the field of view of the AM 17 fits well with the assumption that the coordinates “elevation angle and azimuth” were indeed used.

Rough freehand model: Comparison of straight, horizontal flight paths with a circular flight (elevation angle fixed). A horizontal straight line has quite variable elevation angles (descent to the perspective vanishing point)! One looks slightly from below into the horizontal white circle. The wall is vertical. Text on this above.

Reading the Circumference Drum of the AM 17

At the circumference drum, the elevation angle to the aircraft can be read on the left; it changes continuously. Line family: conversion factor — multiplication or division by the cosine of the elevation angle. Numbers in 1/16 degree. At the far left, the handwheel for setting the elevation angle. Text on this below.

At the circumferential drum of the displacement meter, the elevation angle to the aircraft is read on the far left. For this, the aircraft must obviously be in the center of the field of view. Then there is also a family of lines by which the azimuth lead angle can be converted from the “horizontal plane” to an “oblique plane,” or vice versa (multiply or divide by the cosine of the elevation angle). The meaning and geometry of this conversion has not been understood. In particular, the “oblique plane” cannot refer to the oblique plane in space spanned by the flight path of the aircraft and the observation point on the ground. The conversion of the azimuth-angle lead depends strongly on the flight course being flown and cannot be permanently engraved in metal. If the aircraft flies directly toward the ground observer, there is no azimuth lead; if it passes by the observer, the azimuth-angle lead is at a maximum at the “beam” position (shortest distance) and smaller before and after that.

Image source internet: see after the source citations, images on the AM 17.

Delayed by Decades — a Late Afterbirth. Why, for What Reason?

Images of three different specimens of the AM 17 have been found on the internet, all bearing the designation “blc” (code-name principle from Nov. 1940, for Zeiss from Feb. 1941, “manufacturing identifier”), with “T” for “transparent coating,” i.e., with coated lenses (from 1936), and all with the Reichsadler (imperial eagle) with swastika. Not all of this information can be simultaneously incorrect. The Reichsadler in particular looked quite different under the Imperial era.

Image sources: As with the AM 17 photographs. Below: the eyepiece; to the right: the handwheel.

Strange… the AM 17 was already manufactured in 1916/1917 — and then again more than 20 years later, when fire-control systems operated completely differently, when indirect laying was the norm, and when real computers were already in service? Were there still many old guns in service that could not be controlled by newer devices — for example, those that had no follow-up pointers or lamp rings, or old sights? Or was the shortage of newer fire-control equipment so great that World War I devices were used and even had to be newly manufactured, just to be able to shoot at all?

According to Ref. 1, p. 43, by 1945 a total of 4,429 Kommandogeräte (fire-control computers) had been delivered by Zeiss (destroyed ones must be subtracted from this, the same for the guns). According to the Lexikon der Wehrmacht: 20,750 guns of 8.8 cm were produced, or approximately 5,100 batteries. In addition come the other calibers with 10.5 (over 2,600 pieces) and 12.8 cm (1,129 pieces). These are of course rough estimates and do not give a correct picture. In any case there were always far too few fire-control devices — one reads this frequently. Whether that was a reason for the late production of the 1917 displacement meter ??

Puzzles and Wonders Concerning the Auswanderungsmesser 17

The form of the lines in the eyepiece grid (“bell shape”) has not yet been understood. That more degrees per second are covered in the upper part of the field of view is qualitatively correct, but quantitatively not at all. That the curves bulge out even more strongly in the lower part of the field of view is incomprehensible. Cf. the commentary at Ref. 9b, p. 30.
Strange conversion between horizontal and oblique plane at the circumference drum. The azimuth-angle lead at the AM 17 can or must be converted from the horizontal plane into an oblique plane … or vice versa. What is this for, what lies behind it? Nothing is understood.
Difficult reading of two measured values — altitude/azimuth — in the field of view of the AM 17. On the “STOP” signal from the Flak stopwatch, two measured values must be read off immediately — the aircraft flies on and cannot be halted. The convenient “wandering marker” of the AM 16 is no longer present (cf. p. 23).
Late manufacture of the 1917 device with the marking “blc” from Feb. 1941. What was done with these instruments in WWII — when the aiming procedure and guns were completely different ??

Command Panels or Command Discs / Command Sliders

Since the displacement is determined early, the latest possible corrections must be made just before firing using reading curves: in particular, the projectile flight time must be brought to a current value; but also the barrel elevation due to the curvature of the trajectories must still be incorporated. In early devices (e.g., Kommandotafel Jakob), one often sees the entirety of the calculated projectile trajectories printed on a vertical panel, movable in azimuth, on which the aircraft coordinates are then plotted and the missing information read off.

There are computing discs in ever-new attempts — a comprehensive overview and deeper understanding are lacking. Presented here is a rather late command disc for the Auswanderungsmesser 17, as well as further below a patented idea from Sweden that can be followed to some degree. Whether the Swedish model was practically viable and was ever realized remains questionable.

The Swedish idea did not originate from Zeiss and may for that reason have escaped the sparse descriptions. Ref. 1 covers only Zeiss products.

The command disc for the Auswanderungsmesser 17 is a computing panel approximately 30 cm in size, carried by hand by a handle. It is depicted in the Zeiss archives together with the “stabilized AM 17” in a wooden crate (stabilization: probably a naval application). The disc bears the NEDINSCO company logo — NEDINSCO was founded by Zeiss in Holland in 1921 in order to enable research, development, and production despite the Treaty of Versailles, possibly also for import/export. In a collection of field glasses, from the study of a Zeiss catalog, the same printed company logo with the location designation “s’Gravenhaage” (i.e., The Hague) is dated to 1931: http://www.binoculars-cinecollectors.com/html/body_unusual_page_8.html

The disc discussed and illustrated here differs somewhat in appearance from the command disc that was constructed in 1916 by Otto Eppenstein for the “Peres AM 16,” the predecessor of the AM 17 (cf. Ref. 1, p. 13 or Ref. 2, p. 53, my two images AM_ev16_CV). The basic principle is about the same. Biography of O. Eppenstein: Ref. 1, p. 85/86: His highly deserving name had to be silenced within the firm Zeiss. Disc for AM 15: see p. 23.

Principle of the computers of that era, ca. 1916 to after 1921: All mathematical operations were carried out in advance, in calm times. The results are presented graphically so that they can be read easily and quickly according to the current aircraft situation. The handle at the bottom is cut off. Image: Zeiss archive, Ref. 9c. After 1921.

With this disc, the output addresses only the elevation angle and the projectile flight time; the azimuth angle is not considered. The two large, easily readable scales at the outermost positions show the sought values; the “Aufsatzentfernung” (sight range) is an angle. The large scales are rigidly connected to the fine ring “Em. Entf.” (range finder). One side of the disc refers to an “incoming target,” the other side to an “outgoing target.” The following settings are to be made:

a) From the range finder, the slant distance is reported, which is set by turning the fine ring (and the large scales); Min 20 hm = 2 km, Max 80 hm = 8 km.

b) From the range finder comes the flight altitude, which is entered by shifting the slot-slider with its two external pointers. Altitude: Min 1 km, Max 4.5 km.

c) From the displacement meter comes the measured vertical displacement, i.e., the change in elevation angle of the aircraft during the projectile flight time. This value is set by rotating the slot-slider until the lateral, somewhat inconspicuous markings “Regler” lie at the reported value. Min 0 (stationary balloon), Max 40 (units unclear, possibly 1/16 degree). The two scale halves — left (aircraft low) and right (aircraft high) — are a single display.

This value is here called “Regler” — see further below, see Appendix 2. The circumference drum of the AM 17 is clearly inscribed in units of 1/16 degree, but the reading from the line image of the eyepiece is done in “Regler” (vertical) and in A (1/6400) for the azimuth. The circumference drum and the conversion found there are not understood.

d) At the two opposing tips of the outermost scales, the improved fuze time — called “Brennlänge” (burning length) — can be read, as well as the elevation angle to be set at the gun sight, which is composed of the aircraft lead and ballistics: by that much must one aim higher than the line of sight to the aircraft. This angle is named “Aufsatz” (sight elevation) or “Aufsatzentfernung,” just as the additional angle of a rifle sight can be inscribed as a distance. Values for the Brennlänge: 6 to 29 seconds. Values for the Aufsatz-Entfernung: 1.5 to 8 km.

All figures refer to 7.62 cm Flak ammunition: the “preliminary firing tables were shot in November 1916, muzzle velocity 590 m/s” (small text to the left of the impact-distance pointer). It is also noted what is presupposed in the calculations: “10 seconds delay time.” — The marking arrows in the lateral gaps of the large scales are the ends of the flight-altitude slider on the other side, i.e., for “outgoing target.”

In WWI there appear to have been only burning fuzes, not yet clockwork fuzes. Adjustable burning fuzes work as follows: firing pin / primer / firing-pin spring are activated upon firing. The primer ignites a spiral powder ring of variable length, which burns slowly. During fuze setting (tempering), upper and lower parts are rotated so that a variable length of powder channel is created. Difficulty: aging/moisture of the powder/possibly barometric pressure.

e) From the impact distance it can be read from what range firing is possible — for the first time something like a point of impact, but without azimuth or azimuth lead; probably only approximate.

Notable, Strange, and Remarkable Points

??? Nowhere does the aircraft speed enter the calculation. If the aircraft flies directly toward the position (the lead in azimuth and in altitude remains zero), the distance to the point of impact cannot be determined without the speed. Only the initial distance is known, but with ten seconds of waiting time plus the measurement time of the displacement meter, approximately 12 to 15 seconds are “missed”; in this time an aircraft at 200 km/h flies approximately 600 to 800 m.

??? The projectile flight time of the computing disc begins only at six seconds, with large intervals there — i.e., rather estimated. If one assumes a mean projectile velocity in the first six seconds of approximately 470 m/s, the projectile already covers 2.8 km in six seconds. If the aircraft comes closer than 2.8 km to the position, nothing more can be done with the disc.

??? At small flight altitudes (below 1800 m), the impact distance, projectile flight time, and quadrant elevation depend very strongly on the measured altitude lead — both at large and small altitude lead. A slightly inaccurately read altitude lead immediately gives strongly incorrect fuze times and quadrant elevations.

??? The improved projectile flight time and the quadrant elevation are computed on the command disc from the data: flight altitude and the earlier slant distance to the aircraft, as well as altitude lead, determined 12 to 15 seconds earlier. This does not proceed entirely correctly, because two quite different flights both give an altitude lead of zero: a circular flight around the position, or a direct, central approach toward the Flak position, both at originally equal flight altitude and equal slant distance. The projectile flight time does not change at all during circular flight, but changes maximally during a direct approach. The command disc gives for both flights the same projectile flight time and the same quadrant elevation (unless something fundamental has not yet been correctly understood). — These two flights are in any case outside the basic assumptions: h, v = const.

??? Wind effects, temperature effects, or parallax corrections cannot be taken into account, except through very rough empirical corrections estimated at the very end.

??? The naming of the altitude lead as “Regler” may mean that the strange coordinate system with “Regler” (altitude) and “Schieber” (azimuth) should be understood; see Appendix 2. If this system relates only to the local gun sight, the author can imagine that a sensible, subtle consideration might lie behind it. But if the claim were to orient the entire Flak situation — with aircraft, zenith, engagement, etc. — the author must give up: he simply sees no meaning behind this coordinate system.

Here the author examines with curiosity and interest how these computing operations function and whether they are suitable for special flights or not. This is not, however, an appreciation of the overall achievement: how the method proved itself as a numerical approximation and in overall Flak operations can hardly be judged today. All knowledge of the additional rules, qualifications, and rough corrections that were familiar to people at the time is lacking. In Ref. 4 (p. 51, 54), it is recorded that great experience was required at the time for successful fire control. A device a hundred years old can be judged only with difficulty by today’s notions of what a computer should accomplish.

Always remarkable: all these curves and diagrams were without exception calculated by hand, as were the projectile trajectories themselves. There were as yet no analog computers, no digital computers — only slide rules, possibly adding machines, and paper. Twenty years later, the first attempts with mechanical analog trajectory computers began; see the work “Projectile Trajectory Computers” in this series, in which one German and one Swiss device are presented.

Principle and Procedure of Aircraft Measurement, from Acquisition to Shot

Acquisition of the aircraft with the range finder, then also with the gun sight.
Altitude determination with the pendulum altimeter, as well as slant distance (or horizontal distance). Possibly only from a meaningful range onward.
Flak stopwatch set to distance and flight altitude — yields a first, inaccurate projectile flight time to the aircraft (not to the impact point).
Measurement of the displacement — during 1/3 of the inaccurate projectile flight time. Yields short times and high errors for nearby aircraft! Two coordinate differences read off quickly; values passed on to gun and to command panel.
Azimuth lead set at the gun sight, in addition to continuous aircraft tracking.

Ten seconds remain; within this time the following must occur:

Reading at the command panel:
- Better projectile flight time
- Vertical angle to the impact point, including ballistic elevation
- Values passed on to the guns
Setting at the guns:
- Fuzing of shells, loading of guns
- Quadrant elevation at sight (altitude) newly set, in addition to continuous tracking
Trigger the guns — fire! — probably begin with a new range measurement beforehand.

Own Calculation and Error Estimate

That the displacement — as the most sensitive quantity — must be completed ten seconds before the final operations, and therefore begun even earlier, is somewhat irritating, because the values are no longer correct after further flight distance. In a model flight, the error that the too-early determined displacement produces was estimated by hand: flight altitude 2000 m, speed 180 km/h, lateral distance of the map projection 1.5 km, first acquisition of the aircraft 6 km, 4 km, 2 km, 0 km before the turning point and 2 km after the turning point.

Result: The error (difference between the correct and the too-early lead) is surprisingly small, and at the greatest in angular terms when the aircraft is near the Flak position. At earlier or later acquisition, approximately 0.1° error; in the middle approximately 0.5° error — but the hand calculation was always rather uncertain with regard to the correct impact point!

A Comprehensibly Presented Idea for a New Type of Impact-Point Prediction

German Reich, Reich Patent Office Reichspatent No. 374514 / Carl Oscar Clémentz in Malmö, Sweden Device for determining the position and movement of an object in space Patented in the German Reich from 8 March 1917

The following is freely paraphrased, not according to the wording of the patent — only the images are originals from the patent specification. Whether such a device was ever constructed and employed remains unknown.

Overview:

With a main device A and a secondary device B (approximately 5 km away), the same aircraft is sighted — both times with a telescope. At A, a printed trajectory table (with all firing angles, with all projectile flight times) is erected in the vertical plane pointing toward the aircraft, i.e., laterally movable. Through an electrical connection with probably very many wires and numerous electromagnets, it is achieved that rod 5 from the tripod table E always stands parallel to the lateral aiming position of the telescope in B. Directly above point F, at G, is the scale-reduced version of the aircraft’s position. Both telescopes continuously track the aircraft.

Known therefore:

Slant distance (entirely without a telemeter!)
Flight altitude, horizontal distance

Overview with main device on the left, second telescope B on the right (approximately 5 km away). At D the aircraft is real; at G is the scale-reduced position of the aircraft. Ruler 5 is parallel to B–D. The parallel positioning is achieved by means of numerous electromagnets (battery symbol to the right of tripod E). This parallel positioning is described only in the Swiss patent, not in the German one.

Main device in perspective: trajectory table vertical; below it, horizontal scale 58 for azimuth lead and improved flight time (upper left, circles). Below point G, the flight path is recorded on plane 27 with stylus 26, which is periodically lifted by a clockwork mechanism.

Below point G (model aircraft position) is a stylus that traces a track on the base 27: a map projection of the flight path. The stylus is briefly lifted each second by a clockwork with a cam wheel, so that a gap appears in the track.

Known therefore:

Compass heading of the aircraft
Horizontal speed — practical for balloon observations, for wind measurements

Above the writing surface 27 there is a horizontal intermediate scale 58, with drawn-in azimuth lead lines and circular flight-time lines. A small ruler 57 always sets itself parallel to the aircraft course, because a laterally rotatable friction roller 64 from below always keeps it aligned in the direction of flight. Above friction roller 64 is the clockwork 33 with cam wheel 69/70, which on the one hand periodically lifts the stylus, and on the other hand, by alternately pressing various parts, periodically pushes pointer 65 on scale 67 to the current aircraft speed, which can be read there.

Known therefore:

Aircraft speed
Direction from aircraft to lead point

Stylus 26 below the aircraft image point. Clockwork 33 lifts stylus from the writing track regularly with cam wheel 69/70. Friction roller 64 and cam wheel drive the speed indicator with pointer 65, scale 67. Fig. 6 above, right: pointer wheel 66 is periodically pressed against 64.

Ruler 57 always stands parallel to the aircraft track, carried along by friction roller 64. On it the lead is measured. Solid base with electromagnets for the parallel positioning of ruler 5 with the ground plan of telescope B.

Figures from the patent specification.

The projectile flight time to the observed position of the aircraft (i.e., not to the impact point) can be read from the trajectory table. With the flight time and the aircraft speed, the lead and thereby the impact point can be determined on ruler 57 (parallel to the aircraft course) by external multiplication (not entirely correct, because the projectile flight time is not quite right). On the basis of the azimuth lines at scale 58, the lateral angle lead is read.

Known therefore:

Approximate impact point
Azimuth-angle lead (which must still be computed to the final azimuth angle at the gun, or set at the sight in the case of direct laying)

It is now possible to follow from the found impact point on ruler 57 along the printed circle line on scale 58 through the impact point (improved flight time) to the vertical projectile-trajectory table, then vertically upward, and at the known flight altitude near point G one can read off the necessary vertical angle of the gun, including the ballistic elevation.

Known therefore:

Vertical angle of the gun
Fuze time

Phew… all this in a few seconds, in wind, on uneven terrain, with rain-fogged glasses???

Somehow everything seems shaky. Logically sound, mathematically perhaps a good approximation — but probably only realizable under laboratory conditions. This is an attempt… real computers urgently needed to be developed that would independently calculate all of this according to this procedure. Here people always “read off,” set parallel, aim — and in the end the impact point and the gun angles are indeed found, entirely without a telemeter, without any displacement meter. Graphical representations everywhere. Positional differences between the computing device and the guns, as well as daily influences (wind, temperature), remain unaccounted for. This is not yet a machine calculation; almost every action and reading is carried out by a person. In barely 20 years, the functioning computers that do exactly this will be here!

The recording of the flight track and the measurement of the speed have constructive similarities to later solutions in Kommandogerät 36 (flight direction table) and in the Hungarian Gamma-Juhász device (horizontal speed meter, flight direction roller on the base plate).

A Single Sub-Problem Solved in a Completely Different Way: Reichspatent for a Displacement Computer, January 1917

A maverick for this era?? This is already a real computer! A prophet, an erratic block, an early outlier? Or simply a witness to our current ignorance?

What follows has nothing at all to do with the Auswanderungsmesser 17.

In a patent search (address see after the sources), the idea was found for an early computer that determines the displacement (i.e., the angular lead) of an acquired aircraft purely mechanically and in real time, processing continuously changing variables. Whether a corresponding device was ever constructed, or whether the idea remained on paper, remains open. This was almost ten years before the British Vickers Predictor, which is regarded as the first major Flak computer in Europe: it is said to have entered service in 1928, GB Patent 236250 in the year 1924. The computer discussed here handles only a very small sub-problem and cannot be compared with the Vickers Predictor. Nevertheless: this type of thinking is already documented for 1917!

In Berlin-Friedenau there were also the Goerz-Werke — 1911: 2,500 employees, in WWI up to 12,000 — and later the Askania-Werke, both heavily involved in military production and active in air defense through WWII as well. The Askania-Werke appear to have grown out of the firm Carl Bamberg. At the time of WWI, the Treaty of Versailles did not yet exist to create problems for German armaments firms. Later, shell companies were established, e.g., the Dutch NEDINSCO for optical products by Zeiss, or for guns by Bofors/Krupp; cf. Ref. 1, p. 19, 20. Historical information on the firm Carl Bamberg, from which the Askania-Werke later emerged: http://www.friedenau-aktuell.de/ehrenwerte-friedenauer/carl-bamberg/ / http://imt-museum.de/de/das-museum/ausstellung/automatisierung/askania-berlin

Patent texts are often difficult to understand; therefore a new explanation of the device’s functioning follows here.

Functioning of the Displacement Computer

In the top view (Fig. 1), two rollers 1 and 11 can be seen, rotating at constant speed. Two small wheels 2 roll on these — barely visible, just to the side of the axles 3 and 3’, to which the prominent oblique pointers 9 and 9’ are attached. If both rollers 1 and 11 in Fig. 2 rotate counterclockwise, both small friction wheels are pulled to the left — i.e., both pointers 9 and 9’ set themselves to the center position (horizontal in Fig. 1).

Now the entire pointer units are also displaceable parallel to the rollers 1, 11 along guide rods 5 and 5’, driven by one each of the variables measured in the field; according to the patent text, these would be: slant distance and azimuth (at elevation angle and azimuth, the outputs could be fed directly to the guns as leads). If the entire pointer units are displaced at constant speed, the small friction wheels 2 will set themselves to a constant angle relative to the rollers, corresponding to the ratio of displacement speed to rotation speed of the rollers. The pointer thus shows the rate of change of the flight variable — e.g., the angular velocity, if an angle controls the displacement of the pointer units.

A product is now also formed:

The lead angle, by which the guns must be directed ahead of the aircraft, is composed of the angular velocity and the projectile flight time. If, for example, the aircraft moves across the sky at 1.5 degrees/second, and the flight time of the shells is 8 seconds, that gives a total of 12 degrees lead. This can apply (depending on the gun sight) in the oblique plane, with a single angular velocity, or twice individually — horizontal and vertical.

The roller assembly with its displaceable pointer axis yields a pointer deflection (angle of the pointer) proportional to the angular velocity. In order to also form the product with the flight time, the pointer is read visually at scale 10 or 10’, but this scale itself moves on a further carriage more or less away from the pivot axis of the pointers, depending on the projectile flight time, which is set by hand. Thereby, from a continuously changing angle at which the aircraft appears in the sky, the value for the fully calculated lead angle has been determined. This must be envisaged such that initially all values were turned in by hand, read visually, or passed on by shouted commands. Later, electrical methods were found for data transmission, so that cables could be laid (telephones or electrical synchronous transmissions to the guns, with alternating current).

The further long roller 13 on the far left is already controlled electrically according to the elevation angle of a theodolite aimed at the aircraft (elevation angle). The roller is printed with a line pattern. If the left roller 1 is controlled by the slant distance according to the patent description, the flight altitude can be read directly from the line pattern using the distance pointer 15 — a mechanized altimeter.

Noteworthy: In this device, the rate of change of two variables is first determined (the mathematical operation of “differentiation”). This is not otherwise so willingly done, because this operation produces strongly fluctuating outputs from fluctuating input quantities. The valueless fluctuations due to imprecise data can change faster than the important information itself, which can have fatal effects at the output. As long as a person reads and passes on the output, the fluctuations can be averaged out by eye or with a steady hand.

Otherwise one prefers to apply the opposite operation — “integration” — which balances and averages out the inevitable fluctuations.

First Steps Toward Heavy Anti-Aircraft Defense in Switzerland

Information from Ref. 8, from the Federal Archives, a little from Hermann Schild, “Fliegerabwehr,” and from H. Born, “Die geschichtliche Entwicklung der Flab.”

During the First World War, Switzerland has its first heavy anti-aircraft defense. Everything still runs under the name and organization of the artillery. Initially, suitable guns for air defense are lacking. The 7.5 cm field gun 1903 L30 was somewhat improvised, rebuilt into anti-aircraft guns — which, despite severe elevation restrictions, could also fire steeply upward.

Gun Used

1903: The Krupp field gun can fire in elevation only up to 240 A, which is 13.5°. In Switzerland it is the first gun with barrel recoil! This means that it can fire several shots at the same target without the gun needing to be re-aimed — allowing a higher rate of fire. Without barrel recoil, the shot would tear the entire gun from its carefully oriented position. Laterally, with the Krupp gun, a change in barrel direction of only ±3° is possible (not yet a splayed carriage!): truly not ideal for combating aircraft!

1922: Rebuild to 400 A in elevation. 1927: The wheels are additionally placed on elevation blocks; altitude now up to 822 A. 1940: The gun is mounted on a splayed carriage. So much for the artillery sector, i.e., for engaging ground targets.

Anti-aircraft, 1916: The gun is placed on a high turret frame, which as a whole is pivotable laterally on a pivot, 360°. In elevation, from 210 A up to 1140 A are now possible, i.e., 12° up to 64°. The azimuth of the turret structure and the elevation angle of the gun are adjusted with handwheels. To the weight of the gun come the wooden turret, the personnel on it, and certainly also ammunition. Ten batteries of four guns each are built this way (1917). Occasionally, after the location of the first trial battery (1915, 1916) or the fortress guns of the same type, the name “Gotthard-Kanone” is also found. During border violations in the Ajoie, the guns are relocated in 1916 to the Jura, where they came into action a few times — still without a promising firing procedure. In 1919 the Chief of General Staff requests their dismantling (book by H. Schild) — but the tables with the distance corrections discussed below are dated later (14.3.1925 or 1926 or 1928; on the author’s photograph from Ref. 8, the year is not clearly legible). In the book by Brigadier H. Born, “Die Geschichtliche Entwicklung der Flab,” one learns of a training course in 1927 in Airolo with “a 7.5 cm field gun on a wooden frame with all-around carriage” (p. 38); thanks to a cableway, fire could be directed at moving targets.

Alongside this, the infantry anti-aircraft also practiced — improvising with machine guns and carbines to direct fire at the flyers — lying on their backs, or supported on beams … almost hopeless?

Three images of these early 7.5 cm guns have been found: from Ref. 8, A. Wüest, internet.

These guns must not be confused with the 7.5 cm Flab Kan 38 of the Second World War!

At mid-left: the handwheel for vertical adjustment (the breech ring is raised); at right: the handwheel for rotating the turret by means of a rack at the base.

Four operating personnel must ascend the stairs for the aiming procedure and for loading. To the right of the wheel, the sighting device for the layer.

Lower inclination — the gun stands farther forward, since the carriage at the rear is drawn vertically upward. A counterweight at the front facilitates this vertical movement.

A model of this construction stands at the Aviation and Flak Museum in Dübendorf. At the Château de Morges stands a 7.5 cm Krupp field gun 1903/1940 with later splayed carriage and new wheels. Its barrel is probably identical to the old Flak gun: length = 30 times the caliber. The last surviving original 7.5 cm field gun by Krupp 1903 stands in Thun, with a newer aiming device. The gun without gun shields weighs approximately 1,000 kg; the turntable, 1,600 kg. The later 7.5 cm Flab Kan of 1938 weighs 3,100 kg ready to fire and has a barrel length of 49 times the caliber. A fourth image of the turret gun can be found in the Schweizer Aero-Revue No. 11, Nov. 42, Flak issue, p. 436.

[page 19]

Tracking the aircraft jerkily: Standing on the gun mounting are the loader, the breech operator, the assistant aimer, and the aimer — the latter looks through the sight and keeps the aircraft in the crosshairs. Using two handwheels he moves the gun simultaneously in azimuth and elevation. Since the lateral clearance is minimal at only ±3°, a man on the ground must simultaneously rotate the mounting, although he can only aim by improvisation. A second man operates the elevation from below. The aimer at the gun must compensate for the aircraft’s movement, and at the same time also compensate for the movements of his two colleagues on the ground below. Only with very skilled personnel and well-greased bearings will this produce any reasonably smooth motion! — At the same time, the assistant aimer continuously adjusts the sight to set the lateral and elevation lead and the ballistic superelevation.

If an aircraft flying at v = 80 m/s crosses abeam at a range of 4 km, the lateral angular velocity is 1.15°/sec. The loading delay time is prescribed as 15 seconds. From the moment the fuze is set to the moment of firing alone, the aircraft moves 17° in azimuth. During tracking, perhaps even feedback from the aimer at the telescope to the men rotating the mounting was needed — “more azimuth, less elevation”??

Aircraft Measurement, Aiming, and Laying Procedures

>>>> Where to aim so that the aircraft is hit? <<<<

Easily determined data:

The rangefinder / telemeter gives the slant distance to the aircraft.
A pendulum altimeter attached to it (mentioned in Ref. 8) shows the flight altitude. Not used.
The elevation angle of the aircraft can also be read from it, i.e., its angular height above the horizon.
The aircraft’s speed can be estimated, provided its type is recognizable.

From the projectile trajectory curves, for each combination of slant range / elevation angle, the projectile flight time and the required ballistic additional superelevation can be read off (necessary due to the curvature of the trajectory). However, one would need to know the two values of range / angle to the impact point, not to the aircraft. But the impact point is not known; it cannot simply be measured…

The soldiers of that era worked with two tables: a “distance correction table” and a “graphical firing table.” The procedure went roughly as follows (according to Ref. 8, written in 1977, i.e., 60 years after the fact!):

1 Estimating the flight direction with the naked eye: As the gun stands, in the direction of fire, is 12 o’clock. If the aircraft flies past at right angles, one speaks of the direction of 3 o’clock or 9 o’clock. If the aircraft flies directly toward the anti-aircraft position, its direction of flight is 6 o’clock — all relative to the rotating gun, independent of north. The flight-direction estimator continuously judges the direction of flight.

2 Selection of the correct distance correction table; there are tables for estimated aircraft speeds of 20 m/s, 40 m/s, 60 m/s, and finally also for 80 m/s.

3 In the distance correction table, one reads off — at the current slant range (in increments of whole kilometres!) and under the measured elevation angle (every 10°) — by how much the distance from the aircraft to the unknown impact point will change, and what elevation angle the impact point

[page 20 — continued from previous]

will have. The distance correction is to be added to the current aircraft range. The telemeter operator continuously passes on his measurements.

4 In the graphical firing table, one selects the corrected distance (by a radial ruler from the centre) and the new elevation angle to the impact point, and reads off: fuze running time for setting, and the superelevation angle or firing angle — i.e., by how much higher the gun must fire than toward the aircraft. This is a combination of the ballistic trajectory and the lead due to aircraft speed together with the long loading delay time (15 seconds). The superelevation angle is to be set by hand on the sight. Possibly there was a special anti-aircraft sight with larger angle corrections?

5 Using binoculars or stereoscopic telescope, over a period of four seconds (counted verbally: “one-and-twenty, two-and-…”), the lateral lead and the elevation lead of the aircraft are to be measured. These are very roughly converted to the current distance (“times 2, times 3” at 3 km, 4 km) and set on the gun sight. The conversion really ought to have been carried out rather more carefully using a slide rule?

After the firing order, a loading delay of 15 seconds follows to set everything. This additional flight distance is already included in the distance correction table.

The projectile flight time is set on the fuze of the shell; only after that can the gun be loaded. The superelevation angle and the lead in azimuth and elevation are set on the sight. The aimer always keeps the aircraft in the crosshairs, following it with the gun. The lead angles set on the sight cause the gun to fire in a direction somewhat different from the telescope line of sight.

After 15 seconds, the gun is fired!

Regulations p. 31 (Ref. 10.d.): “The influence of wind … is also to be taken into account in the lead setting” — unfortunately there is not a single word about how this is to be accomplished. In the major work “Fliegerabwehr” [Air Defence] by Hermann Schild (1982), the entire laying procedure is described simply as: “The firing procedure was extraordinarily complicated and problematic.”

Illustrations from Ref. 8

[page 20: figure only — Distance Correction Table (crossed out where firing is impossible). v = 80 m/s]

[page 20: figure only — Distance Correction Table detail: 1–12 is the direction of flight; elevation angle every 10° (far right: aircraft elevation angle; number in the fields to the right: corrected elevation angle to impact point). +/−: corrected distance to the impact point. With these corrected values of distance / elevation angle one enters the firing table.]

[page 20: figure only — Firing table. Input: corrected distance (radius), corrected elevation angle (circular scale). Output: fuze time up to 15 sec. and superelevation up to 15°]

[page 21]

Critique, Assessment, Evaluation

The measurement and prediction procedure for determining the impact point appears — like the rotating mounting under the gun — somewhat cumbersome. Whereas in Germany the lead (= excursion) in azimuth and elevation is genuinely measured (over an approximated projectile flight time), Switzerland limits itself to measuring distance and elevation angle, and makes estimates of flight direction and airspeed. Then one looks up, from a pre-prepared table of all possible flight configurations, the forecast of distance and elevation angle to the impact point. From this, the table of projectile trajectories provides the firing angle (superelevation angle) and the projectile flight time (fuze setting). The lead in azimuth and elevation is measured / estimated over four estimated seconds using binoculars, then roughly converted to range. All estimates, table operations, and adjustments to the gun sight must be completed within 15 seconds — the corresponding flight distance is already taken into account in the tables.

In any case, an additional complicating factor is that at the time of WW1 there is still no proper anti-aircraft gun capable of firing at high elevation angles. The necessary wooden construction will prove an obstacle to the desirable rapid and precise movements. Only just before WW2 is a genuine anti-aircraft gun with a calibre of 7.5 cm introduced in Switzerland.

Impressions of the correction table: At first one is alarmed by the coarse distance graduation in 1 km steps (large numbers at far left and far right). However, this is less serious than it appears: the distance correction is applied to the specific measured distance, which is itself already more precise than 1 km (e.g., measured 3,600 m plus correction 300 m = 3,900 m). The corrected distance should be of similar accuracy to that originally determined by the telemeter.

The coarse steps in the elevation angle (every 10°) also seem precarious — these are enormous angles, given the hoped-for precision. But: one does not set the elevation angle on the sight (the aircraft is in any case exactly in the crosshairs), but rather the superelevation angle, i.e., the angular excess above the line of sight. A jump in the elevation angle of 10° may produce a jump in the superelevation angle of 6° or only 0.3°. At a range of 4 km a shot could land 25 m too high — that would still be acceptable. It remains unclear how accurately the lead can be determined for the elevation angle and azimuth angle.

Finally, the direction of flight is to be assessed — here the greatest inaccuracy arises. The gun points continuously toward the aircraft and tracks it. Now, with the naked eye, the angle between the aircraft heading and the direction of fire must be estimated. One can imagine a large horizontal clock face, centred at the aircraft’s position, with “12” always pointing away from the gun. Is the aircraft flying toward “2” or “3”?? Due to foreshortening in perspective this may be virtually impossible to distinguish. There is also no fixed reference direction — the imagined clock face continuously rotates with the gun and shifts its centre. There is no contrail to indicate the direction either.

According to Ref. 8, a graphic (perhaps held aloft?) clock face was used to estimate the direction. Ref. 10.d. says nothing of this. A conjecture: Was the centre of the clock face always held directly in front of the aircraft?

If one erroneously selects sector 2 instead of 3, and the aircraft is at 1 km and 3 km range respectively, the result is distances that are too great by 600 m and 1,200 m respectively (at an elevation angle of 30°). The

[page 22 — continued]

shots will go far too high. The fuze time will be wrong by 2 seconds or more than 5 seconds. That is grossly off the mark; these shots accomplish nothing.

Hypothetically: What would have happened if, with good equipment (a clock face on a mobile stand, quickly adjustable in position and elevation, the observer’s head absolutely steady), the direction of flight had been determined considerably more accurately than to ±30°? The table in its received form (Ref. 8) cannot accommodate the refinement at all… The gross errors seem unavoidable!

One should consider whether a second pass through all the measurements / estimates might already be possible before the first shot has even been fired.

A degree of goodwill is needed!

From a distance of 100 years, identifying all manner of inaccuracies is one side of the coin. On the other hand, the improvements over what came before should also be considered — only then does one see the progress of the time:

[page 22: figure — from www.dca-amicale.ch]

Well, that really won’t do at all?? Compared with this technology, the aiming from the clean mounting and the looking up of the required values in the tables is a genuine blessing!

Four similar pictures from France are to be found in the Federal Archive: E27#1000/721#14095#3476* to …3479*

Appendix 1

Designs Found in Germany, in Chronological Order

The Zeiss works were first cleared out by the Americans in 1945, and later also by the Russians. The documentation and records are consequently severely disrupted. In 1946 the Zeiss works and other firms were dismantled. This was about reparations payments. Certain records were removed / rescued during the war.

Excursion Meter AM15 Peres, direct laying

Ref. 1, p. 12/13

Half-binocular with vertical “altimeter” panel, “first instrument,” Autumn 1915 Ref. 2, p. 52

Reticle plate: faint bell curves and fixed, symmetrical circular arcs, more strongly curved at the top (cf. above, p. 5)

[page 23]

Excursion Meter 1915:
Monocular with curved reticle pattern in the field of view. c: quick-sight. d: distance ruler (bright), value is taken from the rangefinder. x: elevation angle reading. v: the flight altitude reading. m, n, w: elevation angle of the telescope is adjustable, by means of a toothed ring at the periphery.
Centre, D: anti-aircraft clock, delivers 1/3 of the flight time (to the aircraft, not to the impact point). The flight altitude and the slant distance are to be set beforehand. The clock provides the start and stop point for the measurement of the excursion (= lead).
Right: command disc, delivers fuze burn time and superelevation height from the flight altitude, the slant distance, and the measured vertical excursion. h: flight altitude scale (slide to f). a: slant distance, set at c. t: excursion curve field (to be set using marker i). m: distance to impact point, informational, when to fire. n: reading of the fuze burn time. p: reading for superelevation angle.

Image: Ref. 9a. Dating as AM 1915: Ref. 1 and Ref. 2

Excursion Meter 16

Image: Zeiss Archive, image 893_9
Immediately after the eyepiece comes an adjusting drum; it is to be rotated using the visible knob so that a thread in the field of view aligns with the direction of flight. Subsequently, by rotating the knob about its axis, a moving marker is continuously kept on the aircraft along the thread.

At the START of the measurement the aircraft should be standing at the centre of the field of view, and the entire instrument is locked. During the measurement the moving marker is always kept tracking the aircraft. From STOP the moving marker is no longer moved; the aircraft moves away — but the excursion horizontal / vertical can still be read off cleanly! A new computing disc is between the optics and the tripod?

In the AM17, the adjusting drum acquires a new variable grid pattern; the reading is therefore no longer so convenient, and the thread and moving marker are dispensed with.

Free-hand angle measurer 16 by Prof. Pulfrich (more for artillery): Shake-free, experimental, no further development. Enemy positions are to be surveyed from a balloon. Sighting a known subsidiary target. Balloon drift… The reading itself is allegedly accurate to within one angular minute. Does not shake more than looking through a window pane. http://www.wehrtechnikmuseum.de/Exponate/Freihandwinkelmesser/freihandwinkelmesser.html

Excursion Meter AM16 Peres

Ref. 1, p. 13

Housing already looks like the AM17. Hand-carried, circular command disc Eppenstein. Possibly already with variable grid pattern in the field of view.

Jacob Command Table 1917, indirect laying, table uses trajectory curves Ref. 1, p. 14, Ref. 2, p. 54

[page 24]

Excursion Meter AM 17 Peres, frequently illustrated, a stable constant?

Ref. 1, p. 13/14

The “regulator curves” in the eyepiece are actively tracked according to the elevation angle, with Ref. 2, p. 52/53

variable curvature. The bell curves are more bulged than before (all
this not fully understood). “By the end of 1916 almost all anti-aircraft batteries were equipped with these instruments.”

For more detailed description, housing shape, grid lines, variable curvature: see above, from page 5. Virtually nothing about it was found in the Zeiss Archive. The AM 17 was newly manufactured again in the Second World War (not fully understood).

Patent DE303943, Excursion Meter 1917, Werkstätten für Präzisionsmechanik Carl Bamberg, Berlin-Friedenau

Mechanical computer for forming the lead. Early technology of this kind.

DEPATIS patent search

Discussed in greater detail earlier in this work, from page 15.

Patent DE374514, Carl Oscar Clèmentz, Malmö, Sweden, 1917: System for the scaled-down reproduction of the flight, with direct reading from pre-computed trajectory curves. The flight course is determined, the range, the speed — all purely geometrically. Discussed in greater detail earlier in this work, from page 12.

DEPATIS patent search

Back-measurer Schönian (undated); in Doc. 79607 clear references

Zeiss Archive, Doc. 79606, 79607

to the command instrument 1919 are found (the flight is internally reproduced to scale,
horizontal floating circle). A precursor to the proper command instrument Sch.? What does the word “Backmesser” mean?

Excursion Meter (or Command Instrument) Schönian 1918, direct laying.

Ref. 1, p. 15/16, with illus.

Quotation from Alfred Muther, from Ref. 1: “The command instrument Schönian exhibited such great advantages that

Ref. 2, p. 54/55, with illus.

it can be described as the first truly usable measuring instrument to have emerged during the war. It delivers the currently valid impact point and the required command quantities faultlessly, and moreover continuously. Even

daily atmospheric influences and barrel wear could be taken into account.” First form tested 1916. Schönian 18: range 2 km to

11 km, altitude 1 km to 6 km, speed up to 50 m/s. Maximum excursion distance 2 km. Used with a graphical projectile trajectory table. Quotation Ref. 1: “However, Zeiss had to discontinue the series production of the instrument that had already been initiated, since the military regulations introduced in the meantime only permitted the use of instruments for indirect laying.” The instrument was therefore converted once more into the “Flak Command Instrument Schönian 1919” (completed only after the war; no troop trials any longer).

Flak Command Instrument Schönian 1919, indirect laying.

Ref. 5, illustrations of it

further below

The target is tracked in a half-binocular; in the eyepiece a mechanical marker (connected
to the computer) is set parallel to the longitudinal axis of the aircraft — the perspective distortion
appears to be compensated again when setting at the “floating circle.” A wind correction
influences the speed of both the projectile and the aircraft, since in wind the aircraft
no longer moves parallel to its longitudinal axis. The aircraft’s horizontal speed, estimated
freely by hand according to aircraft type and set at the knob, is automatically further
adjusted for climbing or diving flight by means of a template curve, as an approximation.

Twenty years later the actual path of the aircraft is measured optically, from which direction and speed are determined. There is no longer any estimation of speed.

There is no actual calculation of the projectile flight time in seconds. However, the speeds of the projectile, the aircraft, and the wind are combined in the same scale, and this ultimately gives the lateral direction and elevation to the impact point. Using this together with the flight altitude (from the telemeter), the projectile flight time is read by eye from the table of projectile trajectories, as is the required elevation of the gun barrels. Together with the reading from an azimuth circle, the three values are called out to the guns. The “mean speed” of the projectile is taken as an approximation from a vertically displaceable template curve (v as a function of flight altitude and elevation angle to the impact point); there are as yet no form-bodies to store functions of multiple variables.

The trajectory table faces downward; in the Schönian 18 it was oriented upward. The intersection of two wires in front of it gives the future impact point. Operation: three men — at the “diagram,” at the telescope, and at the azimuth circle on the tripod. Illustrations below from Ref. 5. At particularly high or low angles “mechanical constraints in the instrument are said to occur,“

[page 25 — continued]

which limit its usefulness. Description by A. Kuhlenkamp in Ref. 5 (1936): “The instrument no longer meets today’s requirements.”

Images Schönian 19: from Ref. 5

Powder temperature: The trajectory curves for summer and winter are computed separately. A 7.62 cm anti-aircraft gun is not exactly the first thing to find on the internet; it is found in Ref. 2 under captured guns (Russia). The Schönian 19 is already a genuine computer in which the continuously changing variables are processed in “real time” and the current solution is always provided. The operators read the finished values from the trajectory table and pass them on to the guns, which is not entirely continuous (by shouting or telephone; no follow-pointers yet). The guns no longer keep the aircraft in their sights, and a lead is no longer set on the sight.

Handgrip 2 for azimuth, 3 for setting the flight altitude. 6 is the “target vector” (direction parallel to the aircraft axis). At knob 9 the called-out flight altitude is set. 5: parallel guides keep the “floating circle” always nicely horizontal. 13 and 14 for setting the wind. No parallax correction is provided for the distance between the computer and the guns. The housing is probably missing from the images. — The instrument is not mentioned in Ref. 2 — i.e., after its development it will not have reached the troops.

Treaty of Versailles 1919 — very severe for German military armament. At Zeiss 93% of total production was in the military sector. Siemens, Krupp, and Zeiss relocated their military production abroad. KOBO Steinle (design bureau) and collaboration with the TH Charlottenburg for Zeiss work; trials with the Navy (prohibited for the Army). Ref. 1, p. 19–21

Command Instrument Pschorr 1927, Zeiss, ten instruments delivered 1930/31

Ref. 1, p. 24

Basis: course and speed of the target.

Ref. 2, p. 86

>>> Optimised Pschorr leads to the large Command Instrument 36 (also known as: P27a) <<<

“The aircraft speed was determined by an AM instrument resembling the AM Peres from 1914/18.” (Strange: admittedly, with elevation angle, azimuth angle, and flight altitude one has sufficient data to determine course and speed — provided the measurements are continuously tracked. But that is not entirely straightforward and has little more to do with the excursion meter. To determine the flight course, in the Command Instrument 36 the map distance and the azimuth angle are continuously plotted on the flight-direction table, then the tangent is laid to the path by hand — and the computer has captured the aircraft course numerically via the rotatable tangent.)

[page 26]

“Tabulator” instrument 1927/28, developed by Zeiss, Major v. Karabetz, first trials 1932. Ultimately lost out to the Pschorr instrument. Ref. 2, p. 86

Command Computer C2, Zeiss, connected with EM 4m, developed 1927, tested 1932, used until 1936/37.

Mechanical computer, switching and functional diagram published in: Ref. 1, p. 21–23

Development of the Command Auxiliary Instrument 35 in the period 1930–35, angular velocity.

Ref. 1, p. 29–34, Ref. 2, p. 88/89

Subsequently in Germany the two large computers produced in high quantities: Command Instrument 36 and Command Instrument 40, both with a rangefinder mounted directly on top. The Command Instrument 40 was probably the first computer designed for curvilinear flight.

The two command instruments 36 and 40 are very extensive computing machines — they cannot be presented here. Describing both computing systems even in outline would be very laborious. The Command Instrument 36 is explained in Ref. 3, pp. 125–136; however, not a word appears there about the Command Instrument 40, probably for reasons of secrecy. According to Ref. 1, over 2,000 Command Instrument 40 units in total were manufactured and delivered by Zeiss. The contemporary description of the Command Instrument 40 in 59 pages can be found at: http://www.cdvandt.org/L-Dv-T-1352-1-Kommandogeraet-40-low.pdf

Appendix 2

A Very Special Coordinate System — A Puzzle for Strong Nerves

In Ref. 6, A. Kuhlenkamp describes, in the contribution “Flak Sights,” a very unusual coordinate system which — if understood — could possibly shed light on some of the peculiarities of the Excursion Meter 17. It is reported here, even though the author himself has understood nothing of it. Anyone who recognises the sense, purpose, advantages, and concrete applicability of these curious coordinates may congratulate themselves — and may attempt to determine whether the not-yet-understood eyepiece lines and the line pattern on the periphery of the AM 17 can be explained by means of them!

On the associated command disc, the elevation lead is called the “regulator” — see above — which would fit with the designation “slider” and “regulator” of the strange coordinate system (instead of azimuth and elevation).

A. Kuhlenkamp describes two different coordinate systems in which the lead of the aircraft can be specified: on one hand, normally with azimuth angle and elevation angle (the specifications for the lateral lead and the elevation lead are “independent” of one another); on the other hand, with an oblique plane — the two specifications are “dependent” on one another, i.e., the lateral value already contains an elevation component. No justification or explanation is given for how one arrives at this coordinate system, or who uses it, why, where, and with what advantages.

The third type, in which the lead is specified as a single number (angle in the direction of flight), is not mentioned by Kuhlenkamp. A description of this third type can be found in the earlier work of this series: 34 mm Command Instrument, a Swiss proprietary development for the 34 mm anti-aircraft gun 38 by the Bern firm Hasler. Whether individual command auxiliary instruments in Germany (so-called angular-velocity instruments) also used this third type of coordinates is not yet known.

In both systems below:
A = Location of the aircraft at the time the guns are fired. T = Impact point, at a later time.

Normal, right-angled system, corresponding to the earth coordinates of longitude and latitude. At the centre of the sphere stands the measurement instrument (excursion meter) as well as the entire anti-aircraft battery. The lateral lead is measured on a circle parallel to the horizon, the vertical lead along a meridian through the impact point. Image 2 top left: The two lead angles φ and δ are independent of one another, i.e., one coordinate contributes nothing to the other direction.

Strange system, in which the lead coordinates are no longer independent, since they no longer stand at right angles to one another. Specification: The lateral lead is measured along an oblique plane A₀–R₀, which intersects the meridian through the impact point T₀ at right angles, is itself also a great circle, and passes through the aircraft position A₀ at the time of firing. The elevation lead along the impact-point meridian consists of two components, because the lateral lead also brings with it some elevation. Instead of “elevation” (angle above horizon), the term used here is frequently “regulator,” one component of the elevation lead is now called “correction regulator,” etc. What does this mean; where does the word come from? The oblique plane does not pass through the impact point, but through the “regulator point” R₀.

Both images from Ref. 6.

[page 27]

With this strange coordinate system, problems arise that appear incomprehensible from the perspective of air-defence operations:

The impact point is not yet known at all: how can the lead coordinates be read off along a particular oblique plane when the plane is not yet known?

The location of the aircraft at the time of firing is also not yet known at the time of measurement. The excursion measurement is to be completed ten seconds before the shot — from then on the aircraft continues to fly until it reaches the firing point A shown above.

With the normal coordinate system too, the firing point A becomes known only at the end — but it is at least established from the outset in which directions the lead coordinates are to be read off / set.

This is incomprehensible — one must ask whether all of this has actually emerged from the requirements of air defence, or in some other context.

In view of the very late, renewed construction of the Excursion Meter 1917 (after 1941), one might ask in great perplexity whether it could possibly have been about more recent requirements (e.g., anti-tank work with anti-aircraft guns?). But: the not-yet-understood grid pattern in the eyepiece of the AM17 appears to date from 1917, as does the conversion of the lateral lead angle from the oblique plane into the horizontal plane (or vice versa). So, no tanks after all…

And then, again very difficult to understand, a quotation from A. Kuhlenkamp, Ref. 6, p. 48:

“With appropriate design of the mounting and arrangement of the sighting device, in the case of the dependent line of sight [i.e., with two dependent lead values, second coordinate system] instead of the lateral angle lead φ, the lead φ’ in the lateral-lead plane, and in addition to the elevation angle lead, the correction regulator δ, is to be calculated.”

The principal task of the mounting is surely to allow a gun to rotate its barrel horizontally and also to adjust it in elevation. Can something there be designed differently?

It was only with the “Seaguard” system that the firm Contraves chose a completely different construction with a 35° tilt, so that a direction of attack “vertically from above” lies in the middle of the normally covered area: “Sea Zenith guns.” This was from around 1983, following the Sheffield hit by an Exocet missile in 1982 during the Falklands War. Such a gun construction is certainly not known in the year 1940.

Seaguard: https://www.hamfu.ch/_upload/SEAGUARD_Schiffswaffensystem_mit_Nahbereichs_-_Abwehrsystem_CIWS.pdf

One more garnish on the subject of oblique angles:

Applies to artillery, not air defence — this has nothing to do with the “strange coordinate system”

In Ref. 7, extensive discussion is given of how, with guns standing at an angle (e.g., in heavy seas), the various set angles begin to interfere with one another, and what can be done about it. With good compensation one can fire at any time; with a less favourable arrangement one must wait until the waves have brought the ship (moving in two directions, at two frequencies) into certain positions.

[page 28]

On the right is the gun; on the left are the fine, precise drive mechanisms of the sighting device. Before one knows it, four rings with cardanic suspension are already placed between the gun and the sight; one has two telescopic sights and five fine angle adjustments to operate — and beside these, of course, the large training mechanisms for the heavy gun barrel.

One must savour the beautiful name:
Inlineable pointer-sighting device with longitudinally inlined cross-inclination!
Understood?? Repeat!

Image from Ref. 7 (1938)

Appendix 3

Period Images — How Time Passes…

100 years is a very long human lifetime — much changes in that time. What follows are some impressions, outside the topic of “aiming and computing procedures in anti-aircraft defence.” One begins to smile at the good old days.

>>> In doing so, one does not forget that these curiosities occurred at a time when, in the neighbouring countries, millions of people were being torn apart by artillery and machine-gun fire, drowned in sinking ships, or had their eyes and lungs burned by the newly invented chemical warfare agents. Despite all these atrocities, the technical development may be documented and considered.

[page 29: figure] The Aircraft Recognition Service FED soon became less
poetic: watercoloured little clouds, edelweiss,
and art nouveau frames disappeared.
Aircraft, from left: (England, cropped),
Germany, France, Switzerland; most important types.
Total image width approx. 50 cm.
Ref. 10.A.

[page 30]

[page 30: figure] Airships of various countries. Left: Liberté (nouv. mod.) and Lebaudy (semi-rigide), France. Right: Zeppelin IV and Parseval, Germany. In the centre of the image, under the Swiss cross, the military kites, les cerfs volants militaires — right at the bottom, the observer floats in the basket! Recommended only under stable wind conditions.

Images Ref. 10.a. Draughtsman: Fus. Falquet, Poste d’Observation Felsplatte, IV. 1916, and August 1915 (above)

Order for anti-aircraft defence in Schaffhausen, 24 August 1916: Verbatim quotations, Ref. 10.a.

Until the men are trained in firing, the cadre always turns out with live ammunition.
(Company office, telephone connections…) In the event of aircraft reports, one is to ask immediately from which direction aircraft are approaching. If the company is on leave, the guard is to be alerted and the officers and non-commissioned officers of the company are to be sought as quickly as possible.
If an aircraft flies directly over the town or vicinity, all officers and NCOs of the company are immediately to come to the billet and fall in with rifle and ammunition. On the order of an officer, the aircraft or aircraft are to be engaged. (Reports to be submitted…)

Hptm. Andenthaler (?), Cdt. I. Coy.

Results of a balloon trial shoot, 3 May 1916. Two balloons of rubberised cloth, 20 m³, and of oilpaper, 17 m³ (the third balloon, a paper Montgolfière, burst at 100 m altitude). Image: The balloon is 2 km horizontally away, 800 m vertically. The scale drawn in at the top runs from −700 m to +200 m, with markings every 100 metres (likewise vertically). 11 shots at the balloon are drawn in. It is not entirely easy to determine the exact position from the ground. Everything would be three-dimensional.

Ref. 10.c.

[page 31]

There are not only marked differences between “before” and “after” — occasionally there are also constants to be observed in military thinking! When the tower guns had been dismantled again and one seriously and afresh considered with what guns a heavy anti-aircraft force should be equipped: Colonel F. Walter, in a 15-page letter of 8 November 1923, sets out his thoughts on the procurement of appropriate armament materiel. He warns emphatically against trying to cover as many possible tasks as possible with a single piece of equipment: Under no circumstances! Even then… Ref. 10.b.

[page 31: figure] An elegant way of exploiting the laws of the lever with locally available material? One can clearly see that the mounting is far too heavy at the rear for rapid / precise movements. Hopefully the gun remains well manoeuvrable with these counterweights! From 18° to 41° in elevation becomes possible if one can lower the mounting end. Genuine anti-aircraft guns are suspended quite differently.

Undated, approx. 1916. Ref. 10.c.

[page 31: figure] Should one make the borders visible, e.g., illuminate them at night? Or precisely not? Here, those who wish to show the border openly have prevailed (could also serve as a signpost!). Often found: at night, lamps are used “in those communes which have electricity.”

Ref. 10.a.

If illegible: The Chief of the General Staff informs, on 22 June 1916, Major v. Bismarck (Military Attaché of the Imperial German Legation) that a border marker has been installed near Porrentruy: a huge wooden cross of 42 m diameter, 2.5 m above the ground on open meadow. In snow it is turned over and appears black.

In October 1925, strong feelings ran high in the General Staff, specifically with the Chief of Military Aviation (G. Immenhauser), when in a lecture Capt. Ackermann (commander of a fighter wing!) put forward the thesis that the shooting of aircraft with rifles and machine guns constituted a pure waste of ammunition and should therefore be prohibited. Lt. Col. Labhart found that such expressions of opinion were inadmissible, because — even if this were true — one could under no circumstances allow the impression to arise that we were completely defenceless against enemy air attack. Nevertheless, Labhart wished to examine this question more closely so that “only one view would be held. … It will not do for the army to hold two views on anti-aircraft defence with machine guns.” — Capt. Magron conducts trials and proves that shooting at

[page 32 — continued]

aircraft is a pure waste of ammunition. Magron has constructed a new machine-gun carriage that meets requirements with regard to field of view and mobility. It is to be studied further. (Possible: perhaps Capt. Ackermann wanted to have more aircraft procured?? Magron was also a pilot.) Ref. 10.b.

Sources

1. Jenaer Jahrbuch zur Technik- und Industriegeschichte [Jena Yearbook for the History of Technology and Industry], Vol. 11, 2008. Verein Technikgeschichte in Jena e.V. Ref. 1 draws, for the topics of the First World War, possibly on Ref. 2 (i.e., possibly non-independent sources!).

2. Otto Wilhelm von Renz, Deutsche Flug-Abwehr im 20. Jahrhundert [German Air Defence in the 20th Century], Verlag Mittler und Sohn, 1960.
Interesting source by someone directly involved in both world wars: Renz was born in 1891. This book gives very fine expression to the differing opinions, currents, contradictory orders, etc., of the various service, armament, and command agencies — with restraint, but honestly: valuable! The Speer Ministry frequently appears to have made important decisions even on matters of detail, mostly in the negative; “omnipotence” is mentioned, and “contrary to all reason” (p. 107; see also pp. 112, 113, 119, 121, 128, 135, 173/174, 177). With regard to the measurement and laying instruments of WW1, one remains rather at a loss even with and after this book when it comes to understanding the laying procedure. The book is still obtainable second-hand. Guns are extensively discussed, as are ammunition, searchlights, laying instruments, sound-ranging devices, command instruments of the Second World War, radar instruments, rockets, and visions of the future.
Noteworthy: pp. 147/148: At many higher commands it was believed “that inferior human material could be used in anti-aircraft defence, since after all the command instruments would do everything on their own.” Exactly this was also heard in Switzerland at the time of WW2: if when one shook them by the collar, no wooden leg or glass eye fell to the ground — to the anti-aircraft! Here rather more likely due to the necessary later call-up medicals.
p. 64: “By the end of the war in 1918 it was quite clearly evident that the direct firing method [i.e., gunners keep aircraft in the crosshairs] had to be abandoned and only indirect firing could be considered. Free shooting with ground-observation of the burst points or the tracer was also recognised as inadequate, and was now to be replaced by firing with command instruments. However, the Treaty of Versailles stood as an obstacle in the way of this development work. Only the Navy could operate in this field, etc.” (here: nothing found about the fictitious foreign firms)
One advantage of indirect laying is much rarer misunderstanding about which aircraft is being tracked.
p. 137/138: Trials in 1944 to set the time fuze of the shells correctly only upon leaving the barrel.
pp. 143–145: The new, precise flak sight 41 (20 mm) was not accepted by a training school — the cause of the poor shooting was incorrect range data from the too-small rangefinders. Warning against assessing the shooting by tracer observation.
pp. 148/149: Trials for an electronic command instrument and for an instrument A3, where the computer and the tracking unit were separate.
pp. 149/150 briefly: Flak conversion instrument Malsi, which “could even be used as a firing instrument” (similar to ZZR parallax instrument??).
pp. 153/154: Sound-ranging devices even without searchlights, so that the aircraft are not warned (assessed in Switzerland as illusory).
p. 169: Muzzle velocity measuring instrument with two drillings in the gun barrel.

3. Chief Engineer Dr.-Ing. Alfred Kuhlenkamp, Flak-Kommandogeräte [Anti-Aircraft Command Instruments], VDI-Verlag Berlin, 1943.
A. Kuhlenkamp worked for the Army Ordnance Office and had extensive knowledge. The book is rarely offered second-hand; it can also be found in the ETH Library. A rich mine for the instruments of the Second World War.

4. Dr. Walther Meissner, Entfernungs- und Höhenmessung in der Luftfahrt [Range and Altitude Measurement in Aviation], Springer, 1922.

5. Alfred Kuhlenkamp, “Das Flak-Kommandogerät ‘Schönian 19’” [The Flak Command Instrument “Schönian 19”], Rundschau technischer Arbeiten, Vol. 16 (1936) No. 24, p. 7. Available in the Deutsches Museum Munich. Only one page in a weekly journal.

6. Alfred Kuhlenkamp, Sonderheft Flugabwehr [Special Issue on Air Defence], VDI-Ingenieure, 3rd edition 1940, VDI-Verlag, Berlin.
On page 39, an Excursion Meter AM 17 Peres is illustrated whose peripheral drum has different families of curves from those found on the products discovered on the internet, all of which were manufactured after February 1941. On somewhat more than half the drum length (on the eyepiece side), the 1917 curves are labelled “azimuth graduation in the horizontal”; on somewhat less than half (objective side), a curve field separated from it is still labelled 1917 as “altimeter.” Perhaps on the Excursion Meter 17 the elevation angle was still easier to recognise than on the rangefinder, whereas in 1940 and afterwards this was no longer necessary. — 1st and 2nd editions of the special issue: 1938, 1939.

7. C. Waninger, P. Füsgen, Das Richten der Geschütze [Laying the Guns], Berlin, VDI-Verlag, 1938.
In Ref. 6, A. Kuhlenkamp explicitly refers to this work in the contribution on flak sights. This concerns guns standing tilted and at an angle (on ships, on uneven ground) and how the resulting errors can be compensated.

[page 33]

Air defence is discussed considerably more briefly here. The second coordinate system mentioned by A. Kuhlenkamp is not to be found anywhere in this work (70 pages). — Both authors work for the firm Rheinmetall-Borsig. German thoroughness: many trigonometric equations are solved — always to hundredths of arc-seconds. Two examples, verified with a modern pocket calculator: the last digits are actually correct. This was 1938: how did one calculate with such precision?? In the school logarithm tables of 1962, trigonometric functions were tabulated in steps of whole arc-minutes. 0.01 arc-second = 0.00005° = absurdly precise: >> 0.5 mm / 10 km <<

8. Walter Betschmann, Bewaffnung und Ausrüstung der Schweizer Armee seit 1817 [Armament and Equipment of the Swiss Army since 1817]. Vol. 9: Walter Stutz: Artillerie II, Rohrrücklaufgeschütze der Artillerie und schweren Fliegerabwehr [Recoil guns of the artillery and heavy anti-aircraft defence], 1977.

9. Zeiss Archive, Jena.
9a: Document 69533.
9b: Document 79602.
9c: Image Z 4631_0002 (belongs to “Stabilised Excursion Meter,” Ident. 2473, later command disc Nedinsco / Carl Zeiss).
9a: “Description and instructions for use of the Excursion Meter C/V (AM 16) … and the command disc …“
9b: “Excursion Meter with correction reticle plate,” 3 pages; concerns the grid lines on the AM17: minor errors are discussed, old / new reticle plate, and quite strangely: “The reticle plate is computed for a mean elevation angle of 40°. Its readings in elevation and azimuth are mean values from a whole series of practically occurring cases.” … “At greater elevation angle the deflection of the regulator curves becomes stronger, … whereas the curves for azimuth are practically independent of the elevation angle.” Why the geometry (grid reticle) should depend on a whole series of possible flights, and why a specific flight is measured against quite different flights, appears puzzling. Perhaps one gets further when one considers: the concern is not only with the measurement of the excursion, but also with a prognosis at a later point in time, with a fixed loading time delay of 10 seconds additionally to be taken into account.

10. Swiss Federal Archive:
a. E27#1000/721#15993*
b. E27#1000/721#15994*
c. E27#1000/721#18254*
d. E27#1000/721#8073*

10.d. contains the “Regulations for the 7.5 cm field gun on rotating mounting used as an anti-aircraft gun,” 1918, 40 pp. Idea for the mounting: September 1916, trials: March 1917, delivery of first 6 units: May 1917 (stronger recoil springs still missing).

10.c. contains multi-page reports by Colonel Thum, acting Chief of the KTA, “on the inspection of anti-aircraft guns at the German front,” dated 22/24/26 April 1917. Exhibited there were a Russian pedestal gun 7.62 cm (embedded in concrete), a French anti-aircraft gun 7.7 cm, and a German 9 cm gun without barrel recoil. On this occasion Colonel Thum reports on the basic principles of the German anti-aircraft firing procedure, with a peculiar method of “dispersion” that had never previously been encountered, not even in contemporary German documents. The lead consists of a lateral lead and a range lead. All four guns fire three rapid-fire shots at somewhat different ranges. No dispersion is made in azimuth — “the dispersion is effected along the line of sight by parallel corrections.” In the illustration below, the numbers 42…50 designate the distances in each case. “A fuze-setting machine is not used [for dispersion? i.e., fixed time?]; it would only be advantageous if the dispersion of the burn length were to be effected automatically.”

[page 34]

Attempt at interpretation of this drawing: The aircraft flies to the left along the horizontal double arrow; guns I and III stand to the left at a clearly different position from II and IV. I and III always fire at increasing distances, II and IV always at decreasing ones. The fixed fuze setting is somewhat confusing, but in this way one can fire faster. If the distances are given in hm, and the circles are burst clouds, all fuze settings are the same, all shots are fired at identical intervals, then something does not add up: the spacing of the burst clouds from guns I and III (always firing longer distances) cannot be the same as for guns II and IV (always firing shorter distances). Assumption: all guns stand far to the left outside, in groups of two (only in this way do the distances make sense).

Alongside this, in this report from Germany, there are things that are readily comprehensible. A great deal is computed in very little time!

DEPATIS Patent Search:
https://depatisnet.dpma.de/DepatisNet/depatisnet?window=1&space=main&content=einsteiger&action=einsteiger

Fine images AM 17: http://www.fernglasmuseum.at/museum/zeiss_blc_auswanderungsmesser/zeiss_auswanderungsmesser_am17.html
Under this address a model AM 17 is illustrated which has anti-reflection coated lenses (from 1936). The coding for the name Zeiss on the instrument reads “blc,” which according to one source was the case for Zeiss from February 1941 (the principle of the codes found elsewhere from November 1940). If all this is correct, the Excursion Meter 17 from the First World War was still in use until 1940 and was then manufactured anew — which sounds strange. Were there still entirely old guns in service that could not be controlled by more modern instruments, i.e., which still had no follow-pointers or had old sights? Was the shortage of the newer computers and targeting instruments so great that First World War instruments were used and even newly manufactured, simply to be able to fire in some fashion?

Allan Bromley: British instruments, in service from 1928 (somewhat before the large German computers)
http://sydney.edu.au/engineering/it/research/tr/tr223.pdf

In the British fleet, it appears that guns limited to firing up to +40° elevation were relied upon for a long time. In the following contribution, the 4th paragraph states that the British Navy had the worst anti-aircraft defence of all the powers at the start of WW2 — a strange contrast to the lead with the early large mechanical (land-based) computers. The shipborne computers are possibly a category unto themselves, on one hand because of the stabilisation against waves, on the other because they were very large: size and weight play no role on a ship, but they certainly matter for ground-based instruments. Many particulars on this:

http://www.navweaps.com/index_tech/tech-066.htm
http://www.combinedfleet.com/b_fire.htm

Large ship telemeters (international list): 10 to 15 m. The telemeters were already combined with radar measurements.

Author: André Masson, Langenthal, Switzerland
June – October 2017

This is the tenth work on the mechanical computers of anti-aircraft defence:
First work: Command Instrument SPERRY
Second work: Command Instrument GAMMA-JUHASZ-HASLER
Third work: Various instruments of anti-aircraft defence: distance determination, monitoring and training instruments
Fourth work: Computing with form-bodies
Fifth work: Command instrument for the 34 mm gun (angular velocity instrument)
Sixth work: Early CONTRAVES instruments: Stereomat, Verograph, Oionoscope
Seventh work: Sound-ranging: Elascop and Orthognomos
Eighth work: Curvilinear-flight computer
Ninth work: Projectile trajectory computer