The appearance of production-quality IS-2s changed little throughout their wartime run. Original production forms featured a stepped glacis plate with a smaller gun mantlet while lacking a gun travel lock. In 1944, a revised production model appeared with a smooth glacis plate and fitting the 122mm D25-T main gun capped by a double-baffle muzzle brake. The new D-25T gun sported a semi-automatic breech that streamlined the loading/firing process, allowing tanker crews up to two rounds per minute. The mantlet size was increased and a travel lock was finally added to the rear hull. It was only later in the war that a 12.7mm heavy caliber anti-aircraft gun was mounted to the turret roof to counter low-level aircraft threats.
Once in service, the IS-2 proved a formidable addition to the Red Army inventory and was delivered in large numbers, replacing the formations of KV-85 tanks in the process. Any IS-1 series tanks then in production were completed with 122mm main guns and delivered as IS-2 marks. Those evaluation IS-100 tanks were also fitted with 122mm main guns to become "IS-1B" marks. The IS-2 series then went on to become the definitive IS family mark, especially in its 1944 guise when important factors such as cast turrets were introduced to better the series as a whole. The IS-2 proved highly critical in the Soviet demolition of Berlin to close out the war in Europe.
If the IS-2 maintained any drawbacks it was in her oversized projectile ammunition. The 122mm projectile was operated with a separate charge which added to reloading time for even the most experienced of tanker crews. As can be expected, the projectiles themselves were large and heavy, presenting a cumbersome shape to maneuver from within the tight confines of the turret. Since storage space on any tank was limited at best, the size of the 122mm projectile was certainly a limitation, thusly only 28 rounds of 122mm ammunition were carried.
Concerning the available 122mm shells, the AP (armor-piercing) form proved much less adequate against full-frontal attacks on German Panthers though penetration was still possible. Of note was that in the summer of 1944 to which the Germans had formally switched armor fabrication from manganese to high carbon steel with nickel which essentially led to them being more brittle when struck. Couple this with the 122mm shell and the Soviets assumed their projectile was the difference. Vulnerability of the Panther, Tiger or Tiger II was still along its sides, rear or near the turret bustle. It was actually in the IS-2's use of the Soviet HE projectile that the series truly shined. The HE round proved more than capable of dislodging most any German fortified concentrations. As such, the IS-2 could be depended on as an assault gun along with its tank-killing abilities and this "big gun" approach to such actions was something that even the Germans admired and took note of in their own late-war designs.
Following the war, the wartime IS-2 was due for a modernization of sorts to keep it a viable battlefield component throughout the Cold War years. A modernization program brought about use of side skirt armor protection to the upper portion of the tracks while also adding provisions for the mounting of additional external fuel stores at the rear of the hull. In these updated guises, the IS-2 became the "IS-2M". Other Soviet-allied nations also took delivery of the powerful IS-2 including Cuba, China and North Korea. Soviet/Russian Army forms served well into 1995 despite their World War 2 origins.
The IS-2 was eventually superseded by the improved IS-3 series which further addressed armor concerns based on the actions in World War 2. This version featured a new, rounded cast turret with an overall lower profile. Deliveries began in 1944 but the type arrived too late for active use in World War 2 along the Eastern Front. The IS heavy tank family line culminated with the arrival of the IS-10, the final Joseph Stalin tank - later redesignated as the "T-10".
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