Goals Set by War
Spun once, the flywheel of Soviet design bureaus built up an unseen inertia by the time the war was coming to an end. Designers in Siberia, the Urals, and on the Volga overtook their colleagues in allied and enemy countries. While the first IS-2 tanks were just driving out of the Kirov Factory in Chelyabinsk (ChKZ), the design bureaus of ChKZ and factory #100 already received order #5583 from the State Committee of Defense on April 8th, 1944: design a new heavy tank. An analysis of tanks from early 1944 showed that Tigers could penetrate the cast front plate of early IS-2s from 1000-1200 meters and the Panthers could do it from 900-1000 meters. It was necessary to increase the protection of the IS-2 so that the front of the hull and turret as well as the side of the turret and the turret platform were impenetrable to German shells.
The ChKZ design bureau, headed by N.K. Dukhov and M.F. Balzhi, began its work. Their competitors from factory #100, headed by G.N. Moskvin and V.I. Tarotko also did not sit still.
Competition of Chelyabinsk Tankograds
The situation that developed in Chelyabinsk in the later half of the 1940s deserves a special mention. The decision to spin up tank production at the Chelyabinsk Tank Factory (ChTZ) was made even before the war. On June 19th, 1940, the Central Committee of the Party and Government of the USSR instructed ChTZ to begin production of KV tanks designed by the Leningrad Kirov Factory (LKZ). A special tank department was created at the factory, which included both local engineers and specialists from Leningrad. In August, ChTZ received a KV tank and blueprints. In the second half of 1940, the factory produced all parts locally, and the first ChTZ KV was assembled on December 31st, 1940. A building for a tank assembly plant began construction.
In the summer of 1941, war broke out, and trains of evacuated factories flooded Chelyabinsk. On September 12th, the GKO decided to move Kharkov diesel engine factory #75 to the city, and on October 6th, train cars with LKZ equipment and staff followed them. On the same day, the "Stalin ChTZ" was renamed "NKTM Kirov Factory in Chelyabinsk". The director of the new organization was the former director of LKZ, I.M. Zaltsmann, and the chief engineer was the former chief engineer of LKZ, Zh.Ya. Kotin.
Aside from the aforementioned organizations, Chelyabinsk became the new home for equipment and specialists from the Molotov tool factory, Moscow Red Proletariat tool factory, and the Dynamo tool factory. Later, in 1942, a portion of the equipment from the Dzerzhinskiy Stalingrad Tractor Factory (STZ) was evacuated here. All equipment could not be recovered, as German tanks reached the factory while the evacuation was still underway.
These resources, brought here from the entire USSR, formed an enormous production base, nicknamed "Tankograd". Along with workers and tools, it had the minds that created the best tank engine of the war, the V-2, which went into all heavy and medium tanks and SPGs produced during the war in the USSR. In addition, Chelyabinsk inherited almost the entire engineering team that designed the KV-1 tank.
The new chief engineer of ChKZ, Zh.Ya. Kotin, liked working independently. Using all of his connections in the NKTP, he initiated the creation of an experimental factory within ChTZ, which he headed himself, and where most engineers from ChKZ were transferred, even though physically they continued working at ChKZ. This created two competing design groups which would not allow each other to rest on their laurels.
Difficult Road to Perfection
In the spring of 1944, both groups were given the same task. Factory #100 decided to not deviate too far from their previous design, the IS-2. Instead of one piece, the upper front plate was formed from two 110 mm thick pieces welded together in the middle, sloped in the vertical plane and turned at a large angle. Their top was covered by a roof that was sloped 7 degrees from the horizontal. This design was initially called "hooked nose", but later earned the title "pike nose". The angles to the horizontal and vertical planes forced enemy shells to ricochet.
Factory #100 designers rejected large cast components due to progress in electrical welding at the Paton institute, evacuated from Kiev, as well as the overloaded ChKZ casting plant, which produced IS-2 turrets. In addition, rolled armour has superior properties compared to cast armour.
The Kirov factory design differed in its original flattened hemispherical turret, designed by G.V. Kruchenykh. It housed the same 122 mm D-25T gun from the IS-2. The perimeter armour reached 110 mm in the top and 200 mm in the bottom. The steep angle (60 degrees) of its walls improved the chance of ricochet. The floor of the new tank was V-shaped, which allowed the reduction of vertical hull armour and further reduced the mass of the tank.