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IS-2
Gun choice
Two candidate weapons were the A-19 122 mm gun and the BS-3 100 mm gun. The BS-3 had superior armour penetration (185 mm compared to 160 mm), but a less useful high explosive round. Also, the BS-3 was a relatively new weapon in short supply, while there was excess production capacity for the A-19 and its ammunition. Compared to the older 76.2 mm tank gun, the A-19 had very good armour penetration, similar to that of the effective 75 mm high velocity gun mounted on the German Panther, and delivered 3.5 times the kinetic energy of the older F-34.
After testing with both BS-3 and A-19 guns, the latter was selected as the main armament of the new tank, primarily because of its ready availability and the effect of its large high-explosive shell when attacking German fortifications. The A-19 used a separate shell and powder charge, resulting in a lower rate of fire and reduced ammunition capacity, both serious disadvantages in tank-to-tank engagements. However, the gun was very powerful, and while its 122 mm armour-piercing shell had a lower muzzle velocity than similar late-issue German 75 mm and 88 mm guns, Soviet proving-ground tests established that the A-19 could penetrate the front armour of the German Panther tank,[3] and it was therefore considered adequate in the anti-tank role.
German Army data on the penetration ranges of the 122 mm A-19 gun against the Panther tank showed it to be much less effective when the Panther stood at a side angle of 30 degrees to the incoming round: the A-19 gun was unable to penetrate the glacis plate of the Panther at any distance, and could only penetrate the bottom front plate of the hull at 100 m.[4] It was however the large HE shell the gun fired which was its main asset, proving highly useful and destructive in the anti-personnel role. The size of its gun continued to plague the IS-2, and the two-piece ammunition was difficult to handle and slow to reload (the rate of fire was only about two rounds per minute). Another limitation imposed by the size of its ammunition was the payload: only 28 rounds could be carried inside the tank.[5]
IS-2 Production
The IS-2 had a long 122 mm gun with a double-baffle muzzle brake. This IS-2 model 1944 is recognizable by its flat glacis plate. Compare to the 'stepped' glacis plate of the 1943 model IS-2 at the top of the page.
The IS-122 prototype replaced the IS-85, and began mass production as the IS-2. The 85 mm guns could be reserved for the new T-34-85 medium tank, and some of the IS-1s built were rearmed before leaving the factory, and issued as IS-2s.
The main production model was the IS-2, with the powerful A-19. It was slightly lighter and faster than the heaviest KV model 1942 tank, with thicker front armour and a much-improved turret design. The tank could carry thicker armour than the KV series, while remaining lighter, due to the better layout of the armour envelope. The KV's armour was less well-shaped and featured heavy armour even on the rear, while the IS series concentrated its armour at the front. The IS-2 weighed about the same as a German Panther and was lighter than the German heavy Tiger tank series. It was slightly lower than both.
While the design was good for its time, Western observers[who?] tended to criticize Soviet tanks for their lack of finish and crude construction. The Soviets responded that it was warranted considering the need for wartime expediency and the typically short battlefield life of their tanks.[6]
Armour plan of IS-2, models 1943 and 1944 top and bottom, respectively.
Early IS-2s can be identified by the 'stepped' front hull casting with its small, opening driver's visor. The early tanks lacked gun tube travel locks or antiaircraft machine guns, and had narrow mantlets.
Later improved IS-2s (model 1944) had a faster-loading version of the gun, the D25-T with a double-baffle muzzle brake and better fire-control. It also featured a simpler hull front without a 'step' in it (using a flat, sloping glacis armour plate). Some sources called it IS-2m, but it is distinct from the official Soviet designation IS-2M for a 1950s modernization. Other minor upgrades included the addition of a travel lock on the hull rear, wider mantlet, and, on very late models, an antiaircraft machine gun.
In the mid-1950s the remaining IS-2 tanks (mostly model 1944 variants) were upgraded to keep them battle-worthy, producing the IS-2M, which introduced fittings such as external fuel tanks on the rear hull (the basic IS-2 had these only on the hull sides), stowage bins on both sides of the hull, and protective skirting along the top edges of the tracks.