IS-1 / IS-85 Heavy Tank (Object 237) - Gun
The combat use of IS 1 in the history of the Great Patriotic War was unsuccessful, since the tank’s guns could not always penetrate the armor of the enemy’s combat vehicles. In January 1943, two hulls with a thicker frontal armor and new turrets were expected to be received from the plant No.200 (armored production of the CDC) no earlier than mid-February. This prompted the designers install on one of the hulls of the turret with a 122 mm tank howitzer U-11 design.
V.Sidorenko dismantled an experimental KV-9 heavy tank (Object 229). The logic of this decision was determined by the fact that by this time for the 121.9 mm divisional howitzer M-30 sample 1938, with ballistics close to the prototype U-11, was developed and adopted armament of armor-piercing shells. At a distance of 100 m, this projectile weighing 25.4 kg and the initial at 525 m/s, he punched through a 115 mm armored slab located vertically. The tank with the 122 mm howitzer was designated "Object 234". Ending tests of experimental designs coincided with the first tests against PzKW-VI "Tiger" trophy tanks fired from the main types of guns of the RKKA, gave disappointing results. Thus, in the telephonegram of D.F.Ustinov from February 19, 1943: "The armored hull of the German heavy tank "Tiger" (brow) was said. Armor - 101 mm, board, feed - 82 mm) from a distance of 400-600 m, despite repeated attempts, was not is pierced by armor-piercing anti-tank guns in service with the Red Army...". The most effective were the 85 mm anti-aircraft gun 52-K sample of 1939, 107 mm 1940 M-60 field gun and 122 mm A-19 hull gun of 1931/37. It is significant that out of 15 shots fired from the distance of 400... 600m of 122 mm M-30 howitzer (with ballistics close to U-11) there were no hits at all."
The first tactical and technical requirements (TTT) for the future D-5 were received on March 26, 1943, however, then it was a slightly different gun that had a shorter barrel length and a lower muzzle velocity. Work on the future D-5 system began in April 1943. It was assumed that such a gun could be installed in the standard KV-1s turret and the IS-1 turret. The requirements changed after the shelling of the Tiger were buried. "Full-weight" ballistics 52-K, which allowed penetrating the armor of a German heavy tank, increased the recoil length from the required 350-370 mm to 430 mm.
Between 24 and 30 April 1943, at the armored science test site in Kubinka the Tiger tank was tested with artillery systems armament of the Red Army, and was fired from his 88 mm cannon on armor T-34 and KV-1 tanks. The results of these tests can be judged by the military's note Board of armored and Mechanized Troops RKKA May 4, 1943: "I class" don't punch 100mm T-VI front-line armor from a distance of 500 m... Shooting 82 mm on-board armor the T-VI tank of the 76 mm F-34 tank cannon from a distance of 200 meters showed that Armor-piercing shells of this cannon are weak and when meeting with the armor tank destroy without punching the armor". At the same time, the tank is mounted on the tank T-VI 88 mm tank gun punches the most sturdy frontal part with an armor-piercing projectile The hull of the KV-1 tank is 105 mm thick (75 mm main armor and 30 mm screen) with 1500 meters" Again, the 85 mm anti-aircraft gun 52-K has performed best.
So, from 5 May, after another discussion of problems with the tank and anti-tank artillery, GKO released Resolution No.3289ss "i class" ""On the strengthening of artillery weapons tanks and self-propelled vehicles" , according to which mount in two KB-1S tanks and two prototype IS tanks (objects No.237), 85 mm cannon anti-aircraft gun 52-K and by July 1 to submit them to state tests" .
After a discussion at the OGK NKTP, plant no.100 was assigned to design and manufacture by July 1, 1943 two new tanks, with a mass of no more than the existing mass of the KV tank (46 tons), but powerful frontal armor (at least 100 mm) and the increased diameter of the turret the race. Tank design with 85 mm S-18 tank gun design No.3" ( "Object 237" No.1), a tank project armed with a 107 mm tank gun.
Two prototypes of S-18 (ballistics and ammunition were the same as those of a gun 52-K, and the cradle - like the serial tank gun SIS-5) were manufactured at the factory No.9 Arms (KB had not yet had its own production base), and in the KB plant No.9 they have made a number of changes. V.G. Grabin fundamentally opposed these changes. Factory tests of both guns failed, which Grabin accused the chief KB plant No.9. F.F. Petrov. He blamed Grabin for his failures. Either way, at the factory "Object 237" No.1 with a broken sample of the S-18 gun was testede. In the end, both prototypes of the S-18 gun were modified and installed on prototypes of self-propelled SU-85-1 and SU-85-4.
While the S-18 was being refined, another tank gun was designed in the CAKB, The S-31 cannon was designed to arm heavy tanks. The S-31 was developed in two options - with 52-K cannon ballistics and improved ballistics (initial 880-900 m/s). To do this, the shell casing was used from the cannon 52-K, but the throwing charge is increased. The prototypes of the S-31 were made at the plant No.92. Soon for a number of reasons work on the variant of the S-31 gun with improved ballistics were discontinued, and only the 52-K gun was modified.
By the appointed deadline were made two working guns S-31, based on the results of the test maquette S-18 on the tank "Object 237" No.1. The S-31 cannon was an 85 mm barrel superimposed on a 76 mm cradle tank gun zIS-5, which could significantly facilitate its production and installation in the regular turret KV-1C. The S-31 with a barrel length of 51.2 caliber possessed 300 tsm, which allowed an armor-piercing projectile weighing 9.2 kg and Starting speed of 790... 800 m/s at 1000 m to punch 83 mm armor a sheet at an angle of 30 degrees from the vertical.
When working on Object 237 No.2 due to the impossibility of resuming production 106.7 mm ammunition (stopped at the beginning of 1942) was decided to use D-5T-85 cannon, developed on the basis of the U-12 tank gun design V.N. Sidorenko (The D-5 gun differed from the U-12 mechanism of semi-automatics copy type, borrowed from the instrument of the SIS-5, as well as some nodes rollback brakes and rollbacks) and manufactured by this time in the initiative order in the KB plant No.9. The D-5T gun (initial projectile speed of 792 m/s) was a modified version of the German-type version of the "i class" tank-self-propelled guns" (StuK 40) guns D-5C-85 for SAU SU-85.
By early July 1943 tanks were manufactured at the No.100 plant Object 237 and No.2 with S-31 and D-5T guns, respectively, and at the CDC is a tank "Object 239" (KV-85), a serial KV-1C with a D-5T gun and a tank "Object 238" (in some documents was named KV-85G, i.e. KV-85 with A Grabin a gun) is a serial KV-1C with a S-31 cannon mounted in a regular turret.
Joint tests of the S-31 and D-5T gun systems showed that the main parameters (accuracy of shooting and heaping at a distance of 500... 600 m) they are similar, but the latter had a number of advantages, such as the shorter rollback length and the mass state part, the absence of additional ballast to balance the barrel, denser layout, ease of service, lower height of the line of fire and a smaller vibration of the art system (which has an influence on the heap of shooting at a distance more than 1000 m). In addition, placing recoil devices inside the turret didn't require their outdoor reservations, which made it easier for them to serve and repair and reduced the mass of rolling armor mask gun. Trying to punch The 102 mm frontal armor of the Tiger tank at an angle of 30 degrees at a distance of 500 m failed neither the D-5T gun nor the S-31, while its on-board armor is at the same angle The research calculations of the RESEARCH Institute-48 confirmed that the existing armor-piercing projectile specified the guns can pierce the armor of the specified hardness at a distance of 100 m thick Only 97... 98 mm and 88 mm at 600m.
On 06 July 1943, a new test program was prepared. According to it, it was supposed to make 961 shots from the S-31 cannon installed in the second IS sample, as well as 892 shots from the D-5T-85 gun, which was installed in the first vehicle. The program also included driving tests. The tests took place from 21 to 24 August at the Gorokhovets Artillery Scientific Testing Experimental Range (ANIOP). By that time, both tanks received additional fuel tanks. The S-31 was inferior to its competitor from the very beginning. According to the measurements of the range testers, the recoil length of this gun was 480-570 mm, and this was clearly more than the norm. Also, the disadvantage of the system was the presence of additional weights with which it was balanced. The rollback length of the D-5T-85 turned out to be significantly less - 240-300 mm It turned out to be more convenient access to the recoil devices, due to the shorter recoil, the sleeve catcher turned out to be smaller.
However, in fact, everything was decided before the start of the tests. On August 8, 1943, Stalin signed GKO decree # 3891ss "On the production of KV tanks with an 85 mm cannon (KV-85)." The choice was made in favor of Object 239, which used the same turret as the IS and armed itself with the 85mm D-5T-85 cannon.
This decision was explained by the fact that at the end of July 1943, joint tests of prototypes of self-propelled artillery installations SU-85 and SU-122-III were carried out. The D-5S-85 system became the clear winner on them. So the design bureau of plant No. 9 won the first victory over TsAKB. It is not surprising that the same system was chosen for installation in the KV-85. Sverdlovsk gunsmiths defeated their colleagues even before the start of joint testing of tanks with different weapons.
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