killer" vehicles were introduced by engineer groups from the major Soviet artillery and tank factories. All of these designs used the ML-20 gun as a primary armament, with the KV-1S heavy tank chassis. After some discussion, the project of Josef Kotin was chosen for mass production. This design successfully combined the ML-20 and KV-1S chassis with minimal expense. The project was designated "KV-14" and assembly of the first prototype (called "Object 236") began on December 31, 1942. It was completed after 25 days. Plant trials of "Object 236" began on January 25, 1943. After a number of successful plant tests the more stringent state tests began. "Object 236" succeeded again. On February 14, 1943 the State Defense Committee accepted it for Red Army service and immediately launched it into mass production at the Chelyabinskiy Kirovskiy Zavod (Chelyabinsk Kirov Plant, ChKZ). The designation of the series of self-propelled guns was changed from KV-14 to SU-152. The ML-20 gun was slightly modified for mounting in the SU-152 — some handles were moved for improved gunner comfort. This variant had the designation ML-20S. The muzzle velocity and external ballistics were identical to the original towed ML-20 gun. Although designed with no consideration for the anti-tank role, the SU-152 proved to have surprisingly good anti-tank capabilities due to the ML-20S's extremely heavy high explosive projectiles. Purpose-built anti-tank guns of the period usually relied on small, high-velocity solid projectiles, optimised for punching through armour. Since the SU-152, like all SU-series self-propelled guns was not designed with tank killing in mind, no AP projectiles were issued to crews and no initial tests against armor were conducted. However, tests performed on captured Tiger tanks in early 1943 showed that the SU-152 was able to destroy them at any range with some reliability (in 1943, this is only vehicle in Russian service capable of doing so) by dislodging the turret through blast effect. This discovery spurred massive SU-152 production and the formation of self-propelled artillery units, which then functioned as heavy tank destroyer battalions. After the SU-152 began mass production, it was slightly modified to improve reliability and effectiveness. Initially the SU-152 lacked a machine gun, which was a severe weakness in urban warfare and other close combat. To solve this problem the DShK 12.7 mm anti-aircraft gun installation was developed in the summer of 1943. Some SU-152s received it after repair. The SU-152 was the last member