Prototype KVs

Despite the superiority of the KV over any other tank in armour and armament in 1940, the Soviet Union did not stop developing heavy tanks. Intelligence about thick armour and high penetrating guns of the potential enemy led to bigger and better tanks being developed.

KV-3 (Objects 150, 221, 222, 223)

The first is the KV-3 (Object 150). Unlike the later tank with that same name, this was essentially a slightly better KV-1, with 90 mm of armour and an improved F-32 gun (early KV-1s had the L-11 gun). The KV-3 also had a commander's cupola. However, the thick armour increased the tank's mass to 51 tons, which was too much for the engine. Regardless, the vehicle passed trials. Only one was built before the war. It was lost in battle defending Leningrad with the 123rd Tank Brigade. This tank is also known as "first KV-3", or T-150.

KV-3 (Object 150). The only immediately apparent difference between this and the KV-1 is the presence of a commander's cupola. From Solyankin et al, Soviet Heavy Tanks 1917-1941

KV-3 (Object 221) was developed with an 85 mm gun, but was never built. KV-3 (Object 222) with the F-34 76.2 mm gun met the same fate. In 1941, an electromechanical transmission was developed, but never built. KV-3 (Object 223) was the most impressive of the lot, with up to 120 mm of sloped armour, and a 107 mm ZiS-6 gun. It was never built. However, a KV-1 with a lengthened hull was built, and artificially loaded to 70 tons, in order to see if the torsion bar suspension could handle that kind of weight. It could, but the rubber tires would have to be reinforced.

KV-3 (Object 223). Model and inside. From Solyankin et al, Soviet Heavy Tanks 1917-1941

In April of 1941, it was decided that all KV-3s needed 120 mm of armour in the front of their turret and hull.

KV-220 (Object 220)

The KV-220 was another development of the KV-1. It had unsloped turret armour plates, but a roomier turret, and an 85mm F-30 gun. Armour was improved, up to 100 mm. The tank had an improved transmission compared to the KV-1. The prototype were sent to defend Leningrad with the 124th Tank Brigade, re-equipped with a 76 mm F-32 gun. The old turret was used as a part of an artillery battery. The tank was lost in battle, later repaired, and sent to a training unit.

KV-220. From Solyankin et al, Soviet Heavy Tanks 1917-1941

KV-220 being transported by crane in the background. The seventh road wheel and fourth idler are clearly visible.

An order to assign new vehicles to the 12th Independent Training Tank Regiment. A tank model "For the Motherland", serial number 220-2, engine number 1193-03 is the KV-220 that survived. CAMD RF 3674-47417-2

KV-4 (Object 224)

At the same time, another group of engineers was developing the KV-4. The tank would have a 107 mm gun, a 45 mm gun (76.2 mm in one project), and light and heavy machine guns. Some versions were equipped with a flamethrower. The powerful engine would accelerate the KV-4 up to 51 kph, depending on the project. The armour was even greater than that of the KV-3, at up to 180 mm. The mass of the tank was up to 100 tons. Over 20 designs were proposed, some are available at the Russian Wikipedia page. The most interesting ones are Kruchenyh's design (9 crew members, 180 mm of armour, 107.7 tons), Yermolayev's design (51 kph max speed), Shashmurin's design (76 mm gun in the turret, 107 mm gun in the hull), Mihailov's design (50 kph, 180 mm of armour), and Tarapatin's design (107 mm gun turret with limited traverse). Visually interesting designs are included in this article.

Three designs of the KV-4 by Shashmurin, Tarapatin, and Fedorenko, illustrating the many unconventional shapes a KV-4 could have taken.

KV-5 (Object 225)

The KV-5 projects had the same armament and engine as the KV-4, but even more armour than most of those projects (150-170 mm).  The mass was projected to increase to 100 tons. The project was meant to be finished in October of 1941, but the start of the war interfered. Simplifications to the tank had to be made, such as replacing the stamped turret with a welded one, and a single 1200 hp engine with two 600 hp ones.

The start of the war defined the priorities of KV production.

CAMD RF 38-11355-958

"By order number 1217-503ss from May 5th, 1941, the production of tanks at the Kirov factory is outlined as follows: the primary tank for 1941 will be the KV-3, and, depending on the trials of the KV-4 and the KV-5, one of these three vehicles for 1942. 

The Chelyabinsk Tractor Factory will keep producing the KV-1 with 75 mm of armour. There is a possibility to, without radically altering the production process, to increase the protection of the tank by increasing the armour to 90 mm. 90 mm thick armour that is hardened by high frequency electric current is equivalent to 100-110 mm of armour. 

An experimental prototype of a KV tank with 90 mm of armour is being developed at the Kirov factory, (order number 1288-495ss) that uses the same configuration as the KV-1, aside from the gun. The factory tests are producing satisfactory results. 

Based on this, it is possible for the Chelyabinsk Tractor Factory to, starting with January 1st 1942, begin producing KV tanks with 90 mm of armour and 76.2 mm model 1940 guns. 

This decision will allow for:

1. Increasing the second manufacturing base for powerful tanks.
2. Production of spare parts for existing KV-1 and KV-2 tanks.

Please confirm these developments.

Marshal of the Soviet Union G. Kulik."

However, as the war went on, it became abundantly clear that heavily armoured tanks were to be replaced with fast ones, and powerful expensive new guns were not needed. The upgraded version of the KV-1, the KV-1S, had less armour, and not more. Later KVs with the numbers 6 through 12 were either KV-1 tanks with modified armament or, in the case of the KV-7, a radically different vehicle.