The first tank of the Stalin series, the IS-1 was a direct development of the KV-85, using the same exact turret and 85mm cannon, but with an improved hull and more powerful drive train. In fact, the only reason for the existence of the KV-85, Object 239, is that production of the hulls for the IS-1, Object 237, was delayed by two months. The IS-1 is slightly smaller and more solidly built than the KV-85, with the armour concentrated at the front, both with greater thickness and more severe angles to provide greater protection during the tank's intended breakthrough operation. These changes were further developed after a very short time, as the IS-1 was quickly replaced with the much more powerful IS-2 in late autumn of 1943.
Ordering the small variant will give you a single tank.
Ordering the medium variant will give you two tanks.
Ordering the large variant will give you five tanks.
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