September 12, 1944
To the chairman of the technical Council of the People's Commissariat for Armaments of the USSR, Comrade E.Satel.
According to the results of the test shooting performed against the German Panther tanks at the Kubinka Proving Grounds of the GBTU the guns tested in order of decreasing effectiveness against the frontal armor of the Panther are as follows:
1. The D-25 122 mm tank gun manufactured at the factory #9. Its ballistic characteristics are identical to those of the following guns: the A-19 122 mm, the D-2 122 mm (factory #9) and the S-4 (Central Artillery Design Bureau), giving it a muzzle velocity of 780-790 m/s with a 25 kg projectile. This gun reliably penetrates the Panther's frontal armor at 2500 metres, and that is less than its maximum range.
2. The D-10 100 mm tank gun with ballistics identical to those of the BS-3 100 mm gun, its muzzle velocity being 890-900 m/s with a 15.6 kg projectile. This gun can penetrate the frontal armor of the Panther at up to 1500 metres, which is its maximum range.
3. The German 88 mm gun with muzzle velocity of 1000 m/s with a 10 kg projectile penetrates the Panther's frontal armor at distances of only up to 650 m.
The Panther's frontal armor is 85 mm thick and sloped at 35 degrees to the horizon. Therefore, when shooting at it from the above stated distances the angle of the projectile's trajectory at the point of impact is close to 0 degrees, and the difference between the axis of the projectile and the right angle to the armor's surface (angle of impact) is close to 55 degrees.
The above test results are preliminary, as the testing was done on guns with varying levels of deterioration: the 100 mm D-10 had fired 400 shots, and the 122 mm D-25 was new. However the difference in our test results is so great that it is unlikely that any necessary adjustments will be more than minor.
The method of evaluating armor penetration at angles of impact ranging from 0 to 30 degrees that is currently in use appears to be inefficient in evaluating the anti-tank guns.
Therefore it is our opinion that it is necessary to reconsider the subject of the most effective caliber of the anti-tank guns.
In regards to fighting the Panther tanks the tests at Kubinka clearly show that the 122 mm D-25 gun (V=780-790 m/s; g=25 kg) is superior to the 100 mm D-10 gun (V=890-900 m/s, g=15.6 kg). Also superior to the later are the 122 mm guns on wheeled carriage (the A-19 of the factory #9 and the S-4 of the TsAKB). The 100 mm BS-3 gun turns out to be less effective.
As you know, currently there are available two types of 122 mm field guns of a reduced weight but equal ballistic characteristics compared to the A-19 gun, i.e.:
1. The S-4 122 mm of the CADB, which is due to be delivered for field testing. The S-4 gun has a lot of parts common with the 100 mm BS-3 gun and its production could be begun using the facilities manufacturing the BS-3. Thus currently we are only waiting for the positive test results from the proving grounds and, probably, field tests of this gun.
2. The D-2 122 mm gun of the factory #9, which has successfully completed proving grounds tests on numerous occasions. A series of four D-2 guns is being readied for field testing. I believe that it is urgently needed to consider the task of manufacturing the D-2, in case S-4 does not pass its tests.
The second important problem that surfaced as a result of the tests at Kubinka is that of the high muzzle velocity, particularly the problem of the 85 mm guns with muzzle velocities of 1000-1100 m/s.
The tests have shown the projectile of the German 88 mm gun to have only limited effectiveness when used against the German Panther tank. It is also known that a similar 85 mm gun comes out to be roughly equal in its size and weight to a 100 mm gun with V=900 m/s. Currently 85 mm guns with muzzle velocities of 1000-1100 m/s are being developed by the CADB and factory #9, however their effectiveness against actual German tanks becomes doubtful, especially given the fact that such a gun would require tank turret dimensions no less than those used for the 100 mm D-10 or S-34 guns.
In this regard it appears that after the completion of the Kubinka tests, and if their final results confirm the current data, it would be beneficial to hold a special meeting to discuss further plans for the development of guns with high muzzle velocity.
The only point beyond doubt at this time is the need for increasing the muzzle velocities of the anti-aircraft guns, where it will result in drastic increase in range and reduction in projectile's time in travel to target.
Requesting you further instructions.
Deputy Chief of the Technical Department of the
Peoples Commissariat for Armaments:
Major-General of Engineering and Artillery
Chief of the Test Designs unit: