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The Chieftain's Hatch: US Gyrostabilisers

It is often observed that one way in which US tanks displayed the technological capability of its designers was in the use of gyrostabilisers. These were used by most US tanks of the war. It is also often observed that the troops in the field found it useless or unreliable, and thus disabled it. This is a little odd as the US had had gyrostabilisers in tanks back to the M3.

These reports did not go un-noticed by Armored Board who, in April ’44, being perhaps a bit curious as to whether or not they were squandering money on toys which the troops were not using, looked into the matter a bit. So, over to Armored Board’s report. This is actually a draft, but presumably the final results wouldn’t have been too much different.



1. The “secret” and “confidential” classification of the gyrostabilizer during the early stages of its use was the cause of much ignorance in its employment and maintenance, and led to a hesitancy on the part of officers and men to make any use of it; consequently, when gunnery was attempted, the device was usually inoperative. This led to all but a few organisations abandoning its use. Those few, including the 3rd Armored Division and the 753rd Tank Battalion, have promoted the use of the gyro and believe that it is a useful instrument. The 3rd Armored Division went so far as to devise a very useful gadget, a sliding weight, so designed that the gun could be breech-heavy without the gyro, and balanced with the gyro. When TM 17-12 was published with a statement that the gyro should not be used beyond 600 yards, the men of the 3rd Armored Division were disappointed because they had been using it successfully at greater range. The 753rd Tank Battalion has reported outstanding success in the use of the gyrostabilizer against enemy tanks in Italy.

2. Many reports of the unreliability of the gyrostabilizer in combat areas have been received. This reliability is in all probability caused by:

                a: Old type equipment, now obsolete

                b: Lack of training in simple first and second echelon maintenance.

3.            a. In old type equipment oil leaks occur around piston rods and oil pump shafts even when new. Shaft failures occur in old pumps. The mono-gyro is more satisfactory mechanically than the old double-gyro as well as being better for gunnery because it is relatively unaffected by acceleration, deceleration, and turning.

                b. Accurate operational records maintained by the 768th Tank Battalion and in the Gunnery Department, Armored School, show a very low percentage of maintenance required.

 This maintenance is minor compared to that required by other components of the vehicle.

[Chieftain's note: The report then delves into the nature of the mechanical breakdowns of the old-type systems, it’s not necessary to go into them here]

4. Training is the element now lacking in the use of the gyrostabilizer. This training may be divided into two classes.

                a. Tactical and Gunnery training.

                1)            Insufficient interest in the use of the gyrostabilizer has been present to stimulate the formulation of a doctrine for use of the gyrostrabiliser or to cause investigation of its possibility. Even now, the tactical training in the Armored School and statements in TM 17-12 avoid reference to the use of the gyrostabilizer except for very brief comments. Until a very recent revision of the Armored School Gunnery Course, the use of the tank cannon with the gyro was given emphasis. This use should be secondary to the machine gun, as is now pointed out in school teachings and the revision of TM 17-12. [Chieftain's note: The report repeatedly used TM vice FM, but I presume they mean the gunnery field manual of the same number]

                2) At the present time, the Gunnery Department, Armored School, in cooperation with the Armored Board and the Armored Medical Research Laboratory, is conducting an extensive firing program comparing gyrostabilizer fire with stationary fire. When this firing is completely analysed, it will provide a sound basis for tactical doctrine in the use of the gyrostabilizer. At present, it is reasonable to say that:    

                a) Using the tank cannon, 50% hits may be expected on a tank front at 500 yards, and 25% hits may be expected at 1,000 yards.

                b) Machine gun is effective when used with the gyrostabilizer at any range at which the tracer or strike may be observed.

                3) The Gunnery Department, Armored School, now offers a course in operation and use of the gyro which is as extensive as the length of the course will allow.

                 b. Maintenance Training.

                A number of agencies are now involved in training mechanics who will work with the gyro – Tank Department, Armored School; Gunnery Department, Armored School; Westinghouse School, Springfield Massachusetts; and Westinghouse representatives in the field.

                1) The course for tank mechanics offered in the Tank Department has been short and of little help in actual diagnosis of maintenance troubles. The course has been greatly improved in a reorganization which provides more time and more practical diagnosis work.

                [The next page appears to be missing, however, advice and opinons do appear afterwards]

Tactical Doctrine as taught:

                Firing with the 75mm gun and the cal. .30 machinegun can be effective from a moving tank. Promiscuous use of the tank cannon from a moving vehicle results in an uneconomical expenditure of ammunition. However, remember that the primary weapon in moving fire is the cal. .30 machinegun. Proper use of the gyrostabilizer places effective fire on targets which could not otherwise be neutralized. The modified gyrostabilizer greatly increases the range at which the tank cannon can be successfully employed from a moving tank.

                Have the gyrostabilizer in operation whenever the tank is moving. This gives the gunner a relatively steady field of view. It enables him to keep himself oriented with respect to the terrain and to search the terrain for targets.

                Use the tank gun, the co-axial machine gun, and the bow machine gun in the final assault. Both the psychological and the destructive effect of a tank closing on a position are greatly increased by the use of the coaxial machinegun and the cannon firing HE. The additional fire placed on the position increases the probability of destruction or neutralization of anti-tank weapons and reduces the losses of the attacking tanks. [Chieftain’s note: This appears to be insightful as to why the bow MG was retained through the war even though it was a known weak point: It was, poor though it may have been, likely the most accurate weapon capable of being fired from a moving tank when not equipped with a working stabilizer]

                Use the tank gun against unexpected tank and anti-tank targets, particularly when moving down roads or over smooth terrain.

                Use the coaxial machinegun for reconnaissance by fire while moving. Fire at suspected bushes, hedges, haystacks etc. The tank cannon may be used against suspected buildings.

                The gyrostabilizer is especially valuable in directing fire from landing craft and from amphibious tanks in assaults on beaches.

                The gyrostabilizer training at The Armored School is of two types, training in maintenance, and training in gunnery.

                [Chieftain’s note: At this point, it should be observed that Armored Board decided to use 786th Tank Battalion, in Camp Chaffee, Arkansas, as a test subject for training. Here are the ‘before’ responses.]


                Training in Maintenance: This course consists of training in normal maintenance, trouble-shooting, and first and second echelon repairs. Within the last year this course has been developed to a very satisfactory point. It now graduates mechanics, armorers, and tank commanders who are very well qualified to keep the gyrostabilizer in operating condition at all times.

                Gunnery Training: Training in stabilizer firing has been markedly influenced by the general development of gunnery training at The Armored School. Prior to the early spring of 1943, the Gunnery Department taught functioning and maintenance, not shooting. During the winter of 1942/43 each student fired several rounds from the 75mm and 37mm tank guns from moving tanks using the stabilizer, but it is to be noted that no rounds were fired from a stationary tank at a stationary target. Needless to say, nothing was learned about shooting and effective fire was not obtained with the stabilizer or without it. With the introduction of true gunnery instruction the emphasis was initially placed on basic principles. Development of the advanced phases of gunnery was accomplished progressively. Gyro-stabiliser firing is the most advanced phase of gunnery instruction and did not reach a satisfactory stage of development until about the first of October. Three hundred and twenty-two students have graduated from gunnery courses since that time. [Chieftain’s note: i.e.  about four months as this part of the report was dated late March. It is to be noted that Armored Force was a substantially smaller force, in terms of personnel numbers, than perhaps commonly thought. In all, less than fifty thousand enlisted Army tankers of all ranks saw overseas service in the war from 1941 to 1945. Thus, 322 gunners is a little low for four months, but not obscenely so when one considers personnel distribution to include ‘peak’ enlistment years and troops who were promoted without attending the courses.]

                The present course of instruction for the medium tank calls for one dry run on a course in which the tank moves some 1,500 yards and one preliminary dry run using the .30 cal. machine gun on the same course. This is followed by one more dry run and a run for record. This course is laid out as proscribed in the AGF tank crew gunnery tests. The targets are kneeling silhoettes. The machine gun phase is followed by one dry run and one recorded run with service ammunition. Three rounds of shot and three rounds of HE are fired on the record run. The targets are panels representing the tank silhouettes and anti-tank guns. Each student fires the light tank course as well. This is the same as the medium tank course except that the first dry run and the preliminary firing of the machinegun are omitted. In all the above firing and dry running the student goes through each run once as gunner, once as tank commander, and once as loader.

                The results of the instruction since October have on the whole been gratifying. The students obtain a healthy respect for the effectiveness of the machinegun when fired with the stabilizer, and they acquire some skill in its use. It cannot be said that the course in firing the cannon is adequate to produce satisfactory skill. It does, however, acquaint the student with the gun reaction, with the method of making the recoil adjustment, and gives him training in the technique of observing the effect of the round in spite of the recoil of the gun and the consequent reaction of the gun and sight. Classes average in the neighborhood of 70% scoring the machine gun firing on the basis of the AGF tank crew gunnery test. Classes average close to 60% hits with the tank cannon. The ranges for 37mm and 75mm firing vary from 500 to 100 yards. If the firing could be restricted to zones close to 500 yards, the scores would be appreciably lower, in the state of training developed in these students.

[End transcript]

So, you recall that survey above of the 786th Tank Battalion? They were given an 8-hour preliminary instruction, and then observed for 2,268 hours of gyrostabilizer operation, firing some 300 37mm rounds, 500 75mm rounds, and some 40,000 rounds of machinegun ammunition over the next five weeks. Once the test period was over, they were asked another question.

The lesson to be learned, I guess, is one we should already know anyway: It doesn't matter how fantastic the piece of equipment is that you give a soldier, if he doesn't have competence and confidence in its use, it may as well not be there. Training is as much about getting confidence in your equipment (The gas chamber in Basic Training? It's officially called the Mask Confidence Course) as it is in making sure you know how to use it. And then it has to be considered important enough to keep maintained. One is reminded of the M-16 debacle when troops didn't maintain them properly, they under-performed, and then the rifle had an uphill struggle to fix its reputation. So it seems that there was nothing wrong with the stabiliser, only with the soldiers who, for no particular fault of their own, didn't know how to use it.

Click Stable Bob for a link to the semi-stable conversation on the forum.

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