Anti-aircraft / Flak special watches from the Reichswehr era: Leonidas, Carl Zeiss

 

During my research for this article, I interviewed several World War II anti-aircraft specialists. I was surprised that none of them were familiar with such clocks. Only later did I learn why: The system had been discontinued by 1936/37.

Already during the 1870/71 war, attempts had been made to shoot down the free balloons the French were using to reach unoccupied territory from the besieged fortress of Paris. Krupp 3.7 cm cannons mounted on four-wheeled horse-drawn carts were used for this purpose. The attempt was not very successful and thus remained an episode.

After the first Zeppelin took off in 1900, the Wright brothers made the first flight in 1903, and two years later an aircraft covered the distance of 38.9 km, the Prussian War Ministry commissioned the Artillery Testing Commission (AKP) to examine whether effective anti-aircraft defense was possible with the existing artillery pieces. In 1906, the AKP presented a report recommending the development of special guns. It was not until 1910 that corresponding guidelines were issued for the construction of 'anti-balloon guns' (BAK), as these guns were called until the beginning of the First World War. The development was not taken too seriously by the General Staff, so that in 1914 only a small number of BAKs, mainly in the 7.7 cm caliber, were available. Since at that time a maximum flight altitude of 2000 m and a speed of 25 m/sec were permitted. A projectile initial velocity (Vo) of 465 m/sec was considered sufficient. The aiming devices were also more than inadequate: a panorama telescope served as the aiming device; a special attachment for a target height of approximately 1200 m provided the necessary aiming angles in approximate values. Windage and elevation lead were estimated.

The rangefinder (EM) initially used was the 'reverse image rangefinder' used by field artillery. The 1.25 m baseline proved too narrow for anti-aircraft defense, so it was increased to 2 m, and towards the end of the war to 4 m. Meanwhile, the 'space image rangefinder', already in use by the Navy, had also been adopted. Starting in 1915, the devices were also equipped with altimeters. The use of flame fuses did not allow for the precise setting of the projectile explosion time. Time fuses were only introduced towards the end of the war. All this shows that improvisation was a priority at the beginning of the war; on the other hand, air raids using 'air arrows' were already taking place in October 1914, causing significant damage to troops and horses. At the beginning of 1916, experts, primarily engineers from gun manufacturing and the optical industry, were commissioned to develop a crash program to improve the situation. By the end of 1916, new, more powerful anti-aircraft guns were made available to the troops.

A significant contribution to improving the situation was the optimization of the aiming devices. Attempts were made to switch from direct to indirect aiming.

In addition to measuring distance and altitude , troops also required equipment to determine the target's movement and thus the lead for windage, elevation, and fuze position. In addition to target distance, altitude, target speed, and direction of flight, the time required for command delivery and loading delay, as well as the projectile's flight time and the daytime and other special influences on the trajectory, all had to be taken into account. At Zeiss/Jena, where the father of the future Grand Admiral Dönitz served as head of the patent department from 1898, the 'Peres' (AM) movement meter was developed in 1915/16. It could measure horizontal, straight, and uniform target movements. It was improved several times over the course of the war. (There were also other systems named after their inventors, Jakob, Schönian, and Pschorr; however, these cannot be discussed in this work.) The system included, in addition to the AM with built-in altimeter, the rangefinder (EM), and a 'ballistic stopwatch'.

In 1916, Zeiss obtained a Reich utility model for such a stopwatch (see box). The anti-aircraft clocks, which are the subject of this study, are based on this design. The clock's dial, consisting of a printed sheet of cardboard glued to a brass disc, displays lines of equal distance in hectometers (HM), meaning the given numbers are to be multiplied by 100. These are in the form of curves, since the flight speeds of the projectile vary at the same distances but with varying terrain angles.

Measurement procedure: The EM provides the distance at which the flight altitude is read on the altimeter. The lead measurement is performed by determining the target's movement from the center of the grid in the device's telescope during a fraction (1/3) of the projectile's flight time. The measurement time is limited by the stopwatch depending on the height and distance of the target. The measured values of the distance traveled by the target indicate the required lead in the regulator and side sections during the projectile's flight time. The determination of the impact distance, or the required attachment and time for fuze adjustment, is done by reading the corresponding scales on the AM.

Operating the stopwatch: The soldier at the stopwatch starts it at the command of the AM operator. When the specified target altitude is reached, i.e. when the pointer is above the corresponding distance line on the dial, the clock is stopped and the time is communicated to the observer at the AM. To simplify reading, the clock was sometimes placed in a metal case with a slider on the edge with which the target distance could be set. (See Figs. 1 and 2) Fig. 3 shows the interaction of two anti-aircraft soldiers operating the AM B2, a further development of the Zeiss device from World War I, and the ballistic stopwatch. The photo was taken around 1936. A characteristic of this system was that a special AM and a corresponding stopwatch were required for each gun type. Fig. 4 shows the dials for three different stopwatches. The hand rotation is the same for all clocks and is 18 seconds.

The additional information on the dial allows us to narrow down the gun type and its approximate age.

- 10.5cm Flak: The stated V0 of 710 m/sec was increased to 880 in 1938. Since a time fuse was already provided, the clock probably dates back to a gun from the Reichswehr era. This type was originally designed for the navy.

- 8.8cm Flak: This clock was also likely intended for a gun from the Reichswehr era. The V0 of 750 m/sec. was later increased to 82o or 860. Since no time fuse was used, the gun could even date back to World War I. 'Dopp.ZoAz' means: Double fuze without impact fuse. Background: If the fuse used at the time failed to detonate the shell—either because the shell missed its target or because of a technical defect—there was a risk of damage upon impact. Therefore, anti-aircraft shells were often manufactured without impact fuses. 'Sch.T.' stands for a firing table that was different for each gun.

- 7.5cm Flak: 'L/36' is a code for the barrel length. 'Kw. G.14' means: The gun was introduced in 1914 and was mounted on a self-propelled gun. With a V0 of 616 m/sec, it probably dates back to the Reichswehr era. In 1932, the V0 was increased to 825 m/sec. From 1933 onwards, this type was withdrawn from the anti-aircraft program, and the guns were sold abroad, for example to Spain.

Movements used: Two movements from Switzerland were used in Zeiss ballistic stopwatches.

1. A Leonidas 'chronograph-compteur' based on a Unitas movement. (Cal. C 45) This movement was primarily used for military and sports timekeeping in the 1920s and 1930s. In this case, however, only its stopwatch function was required. Consequently, some structural components were omitted. Movement diameter 41 mm, lever-lever escapement. To achieve the 18-second hand revolution, the gear train did not need to be modified: the desired effect was achieved by a shortened, very powerful balance spring. Even today, after approximately 70 years, the watch works very accurately. The watch is started by winding it and initially runs idle. The stopwatch mechanism is engaged and disengaged by pressing the winding crown. (See Figs. 5 and 6)

2. Modified Leonidas Movement 121 based on a Venus caliber. It is a stopwatch with a minute counter and a stoppable balance. On the back of the movement is a container for "spare parts" integrated into the movement plate. A balance staff was included in this container. This is occasionally found in service watches. This watch also completes one revolution in 18 seconds. Since the minute counter is not needed, the parts required for it are missing. Movement diameter: 41 mm; lever-lever escapement, monometallic balance. (Figs. 7 and 8)

All watches are housed in simple, sturdy nickel cases (Fig. 9). Until around 1936/37, the watch was operated with an AM and ballistic stopwatch; then, this system was no longer needed. The "Kommandogerät 36," under development since 1926, took over its role. Scientists from the Technical University of Charlottenburg and the Zeiss company participated in its development. This device achieved a new level of accuracy. An improved version was introduced into service in 1940.
 

I would like to thank: G. Thorban, W. Sünkel/Museum of Historical Military Technology, K. Knirim, GR Lang, G. Niemeyer/Museum of Military History, W. Wimmer/Zeiss Archive, H. Simon/Federal Office of Defense Technology and Procurement, Captain B. Hardtmann/Study Collection of the Army Air Defense School in Rendsburg.

In the April 1996 issue of the Horological Journal, the German anti-aircraft stopwatch was described under the heading "Mystery Stop Watch," but its exact function was not disclosed. As can be seen in Fig. 10, the movement is identical to the Zeiss watches, but the second hand rotates every 12 seconds. "KAS Fl." could be interpreted as "Coastal Artillery School Flensburg." "Ubts" and "Tbts" were designations for anti-aircraft guns used on submarines and torpedo boats.

Source: 'Classic Watches' 5/98 by HJ Kummer