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The KV-1S (skorostnoi/ speedy) was a lighter version of the KV-1 heavy tank, produced in an attempt to improve its performance, but it was an unpopular tank, mainly because it carried the same gun as the older tank.
When it first entered combat in 1941 the KV-1 had been largely invulnerable to enemy tank guns, but it was always slower than the T-34, which carried the same gun. As the Germans produced more powerful tanks and anti-tank guns, more armour was added to the KV-1, but without any increase in engine power, so the later versions were even slower than the original. Even with the thicker armour it was still vulnerable to newer German guns, and had no obvious advantages over the cheaper and quicker to build T-34.
In response the KV design team produced the KV-1S. This was five tons lighter than the KV-1 Model 1942. Part of the weight saving came by reducing the armour back to the original 75mm from the 90mm of later KV-1s. The engine deck was cut down, lighter road wheels were used and a smaller cast turret produced. This also had a better layout. The original KV-1 had a three man turret, but the third crewmen was the reserve driver and rear machine gunner, and couldn’t work as the loader, leaving the commander to carry out that role. On the KV-1S the commander was moved to a new position at the back of the turret, with an all-round vision cupola while the third crewman became the loader. In order to solve some of the mechanical problems with the KV-1 a new powertrain was used, replacing the KV clutch and transmission.
Despite these improvements the KV-1S wasn’t popular with many tank officers, who would have preferred the production line at Chelyabinsk to be used for the T-34. The KV-1S was still slower than the T-34, cost more to build, had the same gun and wasn’t much more resistant to the new German 75mm guns. As a compromise production was split between the KV-1S and the T-34. Production of the KV-1S began in August 1942, and a total of 1,370 were built before production ended in April 1943.
In October 1942 the structure of Soviet tank brigades was changed. Previously they had contained a mix of KV-1 heavy tanks, T-34 medium tanks and light tanks. From October 1942 they were only to contain the T-34 and the T-60 or T-70 light tanks. All KV-1s were to go to tank regiments to be used for infantry support. However some tank brigades did get the KV-1S, and some saw combat in the Stalingrad counter-attack. This included the 121st Tank Brigade, which became the 27th Guards Tank Brigade as a reward for its performance during the campaign. However during the battles of 1943 the KV-1S would prove to be little better than the earlier KV-1s and it would soon disappear from the front line. It did see action at Kursk, where the 53rd Guards and 57th Army Heavy Tank Brigades used it with some success.
An attempt was made to install an 85mm gun in the KV-1S, as the KV-1S-85, but the turret was too small to cope with the heavy gun and the design was rejected. Instead a stop-gap design was produced, the KV-85, which combined a modified KV-1S hull with the IS-1 turret. Only 130 of these were built.
Stats (KV-1S – 1942)
Production:
Hull Length: 6.8m
Hull Width: 325mm
Height: 264mm
Crew: 5
Weight: 42.5 tonnes
Engine: 600hp V-2 engine
Max Speed: 45km/h road
Max Range: 250km road, 160km off road
Armament: 76.2mm ZiS-5 gun
Armour: 82mm max