Iosif Stalin tank

 was a heavy tank used by the Soviet Union, the successor to the Kliment Voroshilov tank, renamed after Joseph Stalin following Voroshilov's fall from grace.

Background
An evolution of the Kliment Voroshilov tank, the Iosif Stalin series of tanks was born at the SKB-2 design bureau at the Chelyabinsk Kirov Plant. The capture of a Tiger tank in early 1943 showed the need for a tank capable of fighting Germany's big cat on even footing. The SKB-2 bureau devised the KV-85, a KV-1 with an 85mm tank gun, to bolster the firepower of Soviet tank units in the summer of 1943 while they worked on a new design.

The first generation IS tank, IS-85 was born out of a cancelled KV-13 prototype, featuring a superior armor layout, better reliability, and a large, three-man turret accommodating the 85mm gun. Pressed into service in October 1943, production lasted until January 1944. By then, the T-34 armed with the same gun was commonplace, and Soviet engineers focused on upgunning the existing tank. The new IS-122 entered service in January 1944, armed with a 122mm gun that could destroy any German tank from well outside their firing range.

The end result was a tank lighter than the Tiger and almost equal to the Panther, at 46 tons, with thicker armor than either of the big cats, and a decisive advantage in firepower. It was also a potent tool for breakthroughs, as its 122mm gun was incredibly effective against fortifications and soft targets. A total of 3 854 IS tanks were manufactured before production terminated in 1945.

IS-1
IS-1, initially designated IS-85, was the first generation Iosif Stalin tank. It was armed with the 85mm tank gun and was quickly matched in terms of firepower by T-34 tanks. With the introduction of the IS-122, IS-1s still on the factory floors were quickly upgraded with 122mm guns.
 * IS-1 Komroti: One of the remaining IS-1s used as a command tank.

IS-2 obr. 1943
The first generation of the IS-2 featured a complex, stepped front hull shape with a small driver's visor, and the A-19 122mm gun. While offering tremendous firepower, the tank suffered from low fire rate due to two-piece ammunition. However, it proved to be a tremendous asset to Soviet tank units on the battlefield.
 * IS-2 obr.1943: The basic tank.
 * Beute Stalin: A captured tank pressed into Nazi service.
 * IS-2 Komroti: A commander's tank.

IS-2 obr. 1944
The 1944 variant introduced late in the year added a number of changes to the design, most notably a simplified, single cast front glacis with an incredible protection of 120mm steel angled at 60 degrees. The A-19 gun was replaced with the D-25T model, improving the rate of fire and fire control.
 * IS-2 obr. 1944: The basic tank.

ISU-152
Зверобой (Zveroboy, lit. beast killer) was a modernisation of the SU-152, created to update the design, since the production of the KV-1S chassis used for the old design was coming to an end. The new assault gun, IS-152, based on the superior IS tank chassis, mounting the ML-20S 152mm howitzer inside a spacious casemate. After trials revealed a number of deficiencies, the design was revised and upgraded, resulting in the ISU-152, accepted for production.

Although it mounted an even more powerful gun than the IS-2, the lack of a turret allowed it to conserve weight and the end design was only a ton heavier than the base tank. It had thicker forward armor and was also cheaper to build. All of these made it an exceptional weapon in a variety of roles, including supporting assaults, urban combat, and destroying enemy tanks. That last role was the source of its nickname, as the ISU-152 could destroy any German tank at range, or at least maul it severely, while remaining safe from return fire.

The only drawback was a low rate of fire, which precluded its use in a traditional tank destroyer role. Despite that, it was one of the most versatile and powerful tools in the Soviet arsenal, and the ISU-152 remained in production and service into the 1960s, with a total of 4 635 vehicles produced.
 * ISU-152: The basic tank.
 * ISU-152 (Fin): A captured unit pressed into Finnish service.

ISU-122

 * ISU-122

ISU-122S

 * ISU-122S