Kliment Voroshilov tank

 was an early heavy tank used by the Soviet Union, named after the people's commissar of defense. The KV series was succeeded by the IS series, renamed after Joseph Stalin following Voroshilov's sidelining after his miserable performance on the Leningrad Front: Despite personal bravery, Voroshilov failed to effectively respond to the Axis advance and was replaced by Zhukov.

Background
One of the most fearsome tanks encountered by the Nazis during Fall Barbarossa, the Kliment Voroshilov was the result of a competition to replace the T-35 multiturreted heavy tank. Selected after extesnive testing during the Winter War in Finland, the KV was ordered into production in 1939, with an initial request for 50 KV s. A rush request for a self-propelled howitzer in 1940 resulted in the creation of the KV-2 152mm self-propelled howitzer on the KV chassis. The original tank was redesignated KV-1.

The tank was a thickly armored beast with a torsion-bar suspension, wide tracks, and capable armament for the time, capable of taking on any tank in the Nazi arsenal. However, it had several flaws: Although it was invulnerable to almost any anti-tank weapon of the time, save the 88mm anti-aircraft guns, it was quite vulnerable to itself: The tank was heavier than most tanks of the time, at 45 tons, had an unreliable transmission, was difficult to steer, and most importantly, had particularly poor ergonomics, even for Soviet tanks.

As such, when its advantage in armor was nullified circa 1943 and the T-34 proved to be just as good and much cheaper than it, the KV series was discontinued, replaced in regular roles by the T-34 and by the IS series as a heavy tank. Before that, though, over 5 000 tanks were produced.

KV-1
The standard KV-1 model, with all the drawbacks listed above.

KV-2
The KV-2 variant was a modification of the Kliment Voroshilov introduced during the Winter War in 1940, mounting a 152mm howitzer in a rotating, armored turret. The oversized turret and high center of gravity made it an unwieldy piece of hardware, while the overstressed engine could only give it a paltry top speed and was prone to malfunctions. Only 300 of these tanks were made and production ceased after 1941 and the evacuation of tank factories to the Ural mountains.
 * Sturmpanzer KV-2(r): A captured KV-2 and one of the very few survivors that made it into 1944. Designated Panzerkampfwagen 754 (r).

KV-1E
The KV-1E was an up-armored version of the tank introduced in 1940, with applique armor applied. The E stands for "ekrany", a Soviet term for applique armor.
 * KV-1E: The standard version.
 * KV-1E KAO (203mm): An artillery observer's tank.

KV-1S
The KV-1S was a lightened version of the KV-1 with thinner armor and a smaller, lower turret meant to increase its speed. The shift to a planetary transmission improved reliability, while the regenerative geared steering made it easier to control. Although over 1 300 were produced, the loss of its distinctive heavy armor coupled with the high price tag per unit called into question the point of having a heavy tank that does not have heavy armor and is in effect a slower, more expensive version of the T-34.
 * KV-1S: The basic version.
 * Klimi: Nicknamed used to refer to two captured KVs - one basic and one S - used by the Finns.
 * KV-1S Komroti: A company commander's tank.

KV-85
The KV-85 was a stopgap upgrade, mating the 85mm D-5T gun in an IS-85 to a KV-1S chassis. Although the resulting tank was an effective counter to the Tiger tanks, it was still a stopgap measure and only 130 were produced between its introduction in September 1943 and end of production in December the same year.
 * KV-85: The base tank.

KV-8
KV-8 was a standard KV-1 (KV-1S for KV-8S) fitted with the ATO-41 flamethrower, mounted in the turret, with a coaxial machine gun and an M1932 45mm tank gun, disguised to look like the regular 76.2mm gun.
 * KV-8: Based on the KV-1 chassis.
 * KV-8S: Based on the KV-1S chassis.

Conversions
Developed basing on the Red Army's experiences during Operation Uranus, the Stalingrad counteroffensive in 1942, the SU-152 was the successor to the KV-2 self-propelled howitzer. Instead of placing the gun in a tall, cramped turret, the ML-20 152mm howitzer was mounted in a casemate built on the improved KV-1S chassis. It offered higher mobility, better armor, and enhanced firepower at a reduced cost, compared to its predecessor, and entered mass production in 1943.

Intended as a self-propelled gun for use against fortifications, no tests against armor were conducted and no armor-piercing ammunition was developed for the howitzer. However, the SU-152 turned out to be an excellent tank destroyer: The amount of high explosive packed into each shell could destroy even Tiger tanks by simply blowing them open with sheer blast force. As a result, SU-152 and its successors were produced en masse and organized into improvised heavy destroyed battalions.

A total of 670 or 704 (depending on source) SU-152s were produced before production switched to the ISU-152 in December 1943.
 * SU-152