INVESTIGATIONS IN GERMANY
TANK ARMAMENT RESEARCH,
MINISTRY OF SUPPLY
SECTION F GYRO-STABILISATION OF GUN AND SIGHT-LINE
Ing. Bode said that he had some time ago designed a tank gun stabiliser, the equipment having been tested in field trials in 1937. In spite of good results the German Army ordered the development to be stopped. The stabiliser consisted of a large gyro-scope mechanically coupled to a 2 cm. gun. The gyro rotor was 23 cm. in diameter and weighed 8 or 9 kg. It was electrically driven from 110 volts, 350 c/s, 5-phase at 20,000 r.p.m. The required electrical supply was derived from a generator coupled to the tank engine.
Stabilisation in elevation only was produced. Laying of the gun was carried out by artificially precessing the gyro frame.
In firing trials with the equipment mounted in a tank, a 100 per cent zone (in the vertical)of one metre was obtained at a range of 500 metres, when the tank travelled at 20-40 km/hr.
Drawings of the stabiliser were said to be preserved in a slightly damaged bomb-proof safe belonging to Anschutz. Arrangements were made for the drawings, together with a report to be prepared by Ing. Bode, to be evacuated to T.A.R. via T-Force, Kiel.
When bombing of Kiel became severe, Anschutz distributed various departments of the firm in outlying districts. Thus, a testing laboratory was established at Preetz, under the direction of Dr. Andreate. The equipment being tested had been made at Eutin (see below) and was of a Naval character.
One item of interest was a stabilised rangefinder of 2 metres base length. This was seen in operation on a test bench and appeared to have a good performance. It was claimed that for +100 of roll the rangefinder remained stabilised within +2 minutes of arc, A description of the equipment was obtained at Eutin (see below)
Four special equipments for testing gyro-stabilised Compasses etc. were seen. Large movements of pitch, yaw and roll can be imparted simultaneously, the resulting performance of the equipment under test being recorded electrically.
The following reports were removed: -
- Description of the Anschutz motor stabiliser with AC controlling motors for 2 and 3 metre rangefinders on box stand (dated 1940),
- Description of the Anschutz-E-remote control.
Phonix Werke, Eutin
This establishment is a subsidiary of Anschutz, Kiel and contains a research laboratory attached to a small factory. Dr. Pistor (Technical Director, previously with Zeiss-Ikon at Dresden), Dr. Schweimer and Ing. Ewers were interrogated.
The stabilised rangefinder (seen at Preetz) was designed by Schweimer and Ewers. Principal interest in the design centres on a pair of special magslips, by means of which movement of the rangefinder table in the vertical plane is measured. The magslip pair has a superposition ratio of 360 to 1, so that, for one revolution of the transmitter, the receiver rotates 360 times, An accuracy of detection on the transmitter of +1 minute of arc is claimed for this magslip pair under static conditions. Dynamic performance is unknown, since the stabilised rangefinder was never required to operate at a frequency exceeding 1 cycle in 7 seconds. The transmitter magslip is designed to rotate through only about 60 degs, spring stops being provided to prevent further rotation.
The magslips are energised by a 120 volts 2 phase 10 Kc/sec. supply, obtained from a winding on a special motor generator, designed to supply the entire equipment. Power consumed is 30 to 50 watts.
One magslip pair was seen, but required repair. The firm was instructed to make these repairs and to forward the magslips to T.A.R. through T Force, Plon.
On being questioned, Dr. Pistor said that little work had been done on the theory of dynamical stabilisation. Dr. Beyerle, a former employee of the firm (now living at a nearby school or vicarage), had written a report on this subject. It was only, however, the first part of what had been originally intended. Efforts have been made by the staff of Anschutz to induce Dr. Beyerle to complete the report, but without success. A copy of the report by Beyerle is to be sent to T Force, Plon, for transmission to T.A.R.
Pistor stated that as far as was known by the firm of Anschutz, no stabilisation of the armament on of the sighting equipment of tanks had been developed in Germany. Kreiselgerat of Berlin (Dr. Gievers and Ob. Ing. Mummert), and Siemens Apparate Und Machinen of Berlin (Ob.Ing, Altvater, Dr. Troger and Ing. Schuchmann) were known to be working on stabilisation problems for the German Navy, and Askania of Berlin (Dir. Hunsch and Ob. Ing. Krussmann) for the Luftwaffe.
Enquiries were made of all persons interrogated to determine whether any work on very high speed gyroscopes had been carried out. Nothing was known of any such work and it was said that a speed of 30,000 r.p.m. had never been exceeded in a reliable gyro. Anschutz bought standard balls from the manufacturers and when necessary polished and adjusted them for fitting in their best ball-races. Limitation of the speed of a gyro was said to be due to the bearings and above 30,000 r.p.m. much trouble had been encountered.
No work has been carried out at Unterluss on the stabilisation of armament in tanks, though the firm had received a rough drawing of a stabiliser for the 8.8 cm. gun in Tiger. This drawing was produced by Kreiselgerat of Berlin and was principally a copy of the U.S. Westinghouse mono-gyro stabiliser for the 75 mm. gun in Sherman (See below: interrogation of Simmer-man).
Dir. Emil Muller said that stabilisation was first considered for tanks in 1944. The requirement came eventually from the fighting troop, and probably passed into the hands of the Waffenamt via the Truppeninspektion and the General Staff. Stabilisation in elevation only was being considered, and was found desirable for the following reasons:-
- Time was lost in halting to fire,.
- Once halted, a tank was a good target, especially if forced to halt in a position not of its own choosing.
Two methods of approach were considered.
- Stabilisation of gun. This approach was abandoned, for the necessary equipment was too large to be fitted into existing tanks, and was also very expensive to produce. It was clear that for this approach to be successful an entirely new design of turret was required.
- Stabilisation of Sight-line, In view of the rejection of (i), concentration was focussed on a stabilised sight-line, with an arrangement to fire the gun automatically as it passes through the sight line. No details were known to Rheinmetall-Borsig, who had only been given external dimensions for working the equipment into a Panther. It was thought that a prototype of the stabilising gear was ready at the makers (Kreiselgerat of Berlin) towards the end of the war. One practical difficulty that occurred with such a system was the rather large slot required in the mantlet to allow the sight (telescope) to move independently of the gun. Drawings of the Rheinmetall-Borsig proposals for incorporating the equipment- in Panther were said to have been at Grumma, but were removed either by U.S. forces or by the Russians.
Krupp, Essen (personnel evacuated to Kettwig)
Prof. Dr. Erich Muller knew that some work had been done in Germany towards the end of the war on stabilisation, but not by Krupp. The Heereswaffenamt had at first not been interested in stabilisation, but towards the end of the war were forced to order developments. Stabilisation became a requirement because with the increasing weight of tanks additional stopping for firing and then starting again produced undesirable wear on transmission, clutch etc. Muller thought it was intended at first to stabilise only the machine gun, with a possibility of extending the design later to the main armament. Wa Pruf 6 were responsible for this development.
The question of stabilisation of tank guns was receiving considerable attention in Germany at the end of the war, and appears to have been stimulated by Russian developments in the same field. Theoretically, it was not considered possible to stabilise a heavy gun to an accuracy sufficient for shooting on the move, but Guderian had no knowledge of any practical tests. German policy was therefore directed to a stabilised sight-line with automatic firing of the gun as it swung through the sight-line. Trials had not been completed at the end of the war, but it was intended eventually to fit this system into new tanks. The firm Carl Zeiss of Jena were probably involved in the development.
Firing on the move without stabiliser had been practised after the Allied landings in Europe against Allied tanks. Success depended on the use of highly trained gunners, who were provided with power traverse and hand elevation.
Ludwig Leitz said that his firm had been directed to incorporate into the optical system of a tank sight a moving part which could be linked to a gyroscopic control and which would provide a stabilised sight-line. This was being worked cut in a periscopic sight W.S.F.3, which had not reached the prototype stage at the end of the war. Two graticules were to be positioned in the focal plane of the object glass, one being fixed relative to the sight casing, the other attached to the axis in the sight controlled by the stabiliser, this latter graticule thus remaining fixed in space. The relative motion of the two graticules would give the gunner warning as to when the gun is about to swing through the line of sight.
NOTE : Further details of the optical features of the W.S.F.3 are given in Section G.
Herr Haass (of Kreiselgerat, Berlin, interrogated at the firm of Leitz at Wetzlar).
Haass worked in conjunction with Leitz on the development of a stabilised sight-line. He gave the opinion that, to stabilise gun and sight bulky equipment is necessary, and in any case it is doubtful whether the accuracy of stabilisation attainable warrants firing the main tank armament on the move. Stabilisation of the sight-line, on the other hand, involves small, light and cheap equipment, because only small loads and inertia are involved. It is necessary with this approach to arrange that the gun fires as it mores through the sight-line, and to make an allowance for the firing interval in terms of the angular velocity of the barrel past the sight-line.
The complete equipment which has been developed to stabilise the sight-line for elevation only is contained in a box about 15 cm. cube. This box is fixed rigidly to the gun cradle. The gyroscope frame is supported on two horizontal bearings in the housing, and carries two gyroscopes, coupled back to back, to give minimum sensitivity to sideways movements of the tank. The frame is coupled through a lever mechanism (giving a 1 to 2 reduction ratio) to the axis of the moving component of the optical system. Movements in elevation of the gun thus produce no movement of the line of sight. The gun is fired by the coincidence of two contacts, the angular position of one being controlled by the gyro frame, that of the other by the position of the gun. The latter contact is advanced or retarded by a rate-measuring gyroscope, contained in the Same housing, to give the required allowance for firing interval.
Haass claimed that this stabiliser system had been built and tested with great success at the beginning of 1945. Leitz modified a T'ZF 12 (a) for the trial, two mirrors, to give a small periscopic relief, being introduced in front of the object glass. The lower mirror was fixed to the sight casing and the other linked to the stabiliser. The first trial lasted for several hours over very rough ground, and Haass stated that satisfactory observation was maintained without any fatigue. The sight-line was stabilised to +/-18 seconds of arc, and on firing an average deviation of +0.5 metres from a target point at 1,000 metres range was obtained (10 rounds).
It was intended that the stabiliser should be used also for firing on the halt, the gun being swung by the elevating gear.
Dr. Zimmerman (of Kreiselgerat, Berlin, evacuated to Versailles)
- Dr. Zimmerman was aware that Haass had constructed, in collaboration with Leitz, a stabilised sight equipment. He too is capable of constructing this equipment, and has forwarded some re-ports on the work of Kreiselgerat On stabilisation to G.S.I. (Tech.), H.Q., B.A.O.R.
Kreiselgerat were instructed to develop stabiliser gear for tanks through Wa Pruf 6 (Major Biersack, and later Inspector Walter); no particular priority was given to this project, which was initiated in 1940. Such equipment was required so that tanks could fire on the move, for "a stationary tank is a good target for an antitank gun." No request was ever made for stabilisation in azimuth, only in elevation.
Design of stabiliser equipment for tanks was mainly empirical, being based on the experience available concerning the stabilisation of heavy masses.
As far as Zimmerman knew, Kreiselgerat was the only German firm
involved in designing stabiliser equipment for tanks. There was a Russian design but this was considered poor.
- First Tank Stabiliser (3.7 cm. gun)
This consisted of twin free-gyroscopes connected directly to the gun. The gyros were artificially precessed by a reversing motor for control purposes, via a differential which also incorporated the hand control. The accuracy obtained was +7 to +/-10 minutes of arc. The equipment was capable of dealing with an acceleration of 50/sec.2 and a speed of 30/sec.; it was used in N. Africa.
- Second Tank Stabiliser (3.7 mm. gun)
This was almost the same in principle as the first, but with modifications of detail. The gyros were artificially precessed fur gun-laying by a continuously running motor acting via a differential brake arrangement controlled by relays. The stabiliser could be uncoupled and thrown over to hand elevation, The power input to the gyros at 260 c/s was 0.35 kVA, and the gyros had 18 cm. diameter rotors working in hydrogen at an excess pressure of 2-lb./in.2 and at 15,600 r.p.m. They took seven minutes to run up to speed.
- Third Tank Stabiliser (5.0 cm. gun)
As for 3.7 cm. gun but with 29 cm. diameter rotors in gyroscopes, which took 18 minutes to run up to speed. The life of the complete equipment was about 3000 hours.
- Stabilised Sight-line (plus firing mechanism for 8.8 cm. gun).
This was developed, because the size of the gyros required for an 8.8 cm. gun (direct stabilisation) would have been excessive. The device was first designed as a stabilised sightline instrument to allow the spotting of targets on the move, with the aid of relatively high magnification and, consequently, small field telescopes. Firing was carried out at a standstill. It also provided an undisturbed sight-line. Zeiss developed an almost identical stabiliser. The optical side of the problem was carried out by Leitz in conjunction with Haass. The outfit was built, tested and approved, and an order for 3000 was placed. Trials were carried out at Kummersdorf, the results of which were embodied in a report now in Russian hands. Results from Zimmerman's memory: -at 200 m., mean dispersion was 30 cm. and at 400 m. was less than double. This was with the tank stationary, so that the figures are a measure of the accuracy of the firing mechanism (controlled by constrained gyro) and of drift due to the free gyro. On the move the results were "good", irrespective of the position of the gun with respect to the hull. Zimmerman was then asked - "How was tracking done?". He replied- "There was no difficulty; except on switching or rapid turning of the tank". The tank speed on trials was "normal". The firing contacts of the improved device, with constrained gyro added, carried all the primer current and the width of one of the contacts was such as to allow automatically for small velocities. No particular effort was made to reduce the firing time delay. The minimum rate measured by the constrained firing gyro was 2 to 3 degrees/sec. The accuracy of the con-strained gyro over the range of 5 to 40 degrees/sec. was about +/-3 to +5 per cent. At least ten stabilised sight-line instruments (ie. without firing contacts) reached "the front", and the device was intended to be standard Panther equipment. The artificial precession control was of the on/off type.
- Electro-hydraulic stabiliser for 8.8 cm. gun in elevation
This had not been put into a tank, but had been given bench tests. It was captured by the Russians just before tank trials were due to be carried out. A constant volume pump with a blow-off valve set at 80 atmospheres was driven by the main tank engine, and the output from the constrained gyro-pick-up (similar to "silverstats") was taken to an improved form of electrically operated hydraulic valve, which controlled the flow of oil to a hydraulic ram driving the gun. The electro-hydraulic valve consisted of an electro-magnetically operated rocking nozzle directing a jet of oil into one or other of two orifices, these being connected to either side of the ram. The maximum movement of the nozzle was about 10, and the device only required an electrical input of milliwatts for full control. The maximum power controlled was of the order of horse-power. Full details of the device can be supplied by Commander Studdert of D.N.O., Admiralty.