In November of 1941, a new assault tank started development in Chelyabinsk. The project started due to a request from Stalin personally in response to the military's desire for the famous Soviet heavyweight, the KV, with increased firepower.
The tank was indexed KV-7. It was to be armed with three guns: one 76 mm and two 45 mm. The guns could fire independently or all at once. SKB-2, led by G.N. Moskvin, was responsible for brining the project to life.
It was physically impossible to fit three guns into a KV-1 turret, so a prism-shaped casemate was used instead. Many elements of the KV's turret were used in its construction: the MG mount, hatches, observation devices.
N.N. Efimov and K.N. Ilyin developed the artillery system, aided by the famous engineer L.I. Gorlitskiy. It received the index U-13. All three guns shared a mantlet. The 76 mm gun was placed in the center, and the 45 mm guns to the sides. Factory trials on December 27th revealed many deficiencies. The aiming mechanism was considered poorly planned, as were the case catcher, gunner's seat, and several other elements.
On January 5th, 1942, a second round of trials was performed. All three guns fired at once only on the third try. The precision at 400 meters was insufficient. Furthermore, the 45 mm and 76 mm guns had varying rates of fire, which cast doubt on the idea of the multiple gun system. The gunner had difficulty using the sight, and it was impossible to use the forehead rest.
On January 6th, Stalin ordered the replacement of the three gun mount with a dual 76 mm gun mount. L. Gorlitskiy developed the U-14 system, using two ZiS-5 guns. It was mounted on the KV-7 instead of the U-13. The casemate remained the same, only the gun and ammunition racks changed.
The double barreled KV-7 began trials on May 16th, 1942. Again, several faults were found. The gun elevation increased after every shot. The aiming mechanisms were very heavy. The cassette based ammo rack was considered unsuccessful, and was replaced with an open crate design.
The second round of trials never started. The Chelyabinsk tank factory threw all its resources at the KV-1S project. Interest in the assault tank waned. Although it still drove over one thousand kilometers to test its improved transmission, its story came to an end at the end of December of 1943. The SPG was disassembled and scrapped. Armour cut up to produce KV-7 hulls was used in other vehicles.
The design of the KV-7 was a mistake. However, its impact on tank building was immense, as it was a pioneer among heavy SPGs, including the legendary "Beast Slayer" SU-152.
Original article available here.