This is a bit of another review than the last few, because of the whole development. We begin with some fourth wall: I made a KV chassis, and then made everything the Russians did with this chassis.
Now we will travel into Soviet Russia, to explain everything!
The original KV is, like you would expect, the KV-1. This is the first Russian heavy tank. But although the KV-1 was very mass produced, the Russians weren't bothered in forgetting the KV-1's chassis, and developed it further.
In World of Tanks the KV-1 is a tier V heavy tank.
Rear of the KV-1.
The development of the KV chassis then got into more heavy tanks. The KV-1S, T-150, and KV-2 were born. The KV-1S was the more manouverable heavy tank, with a very powerful 122 mm gun. The KV-2 was a very big tank with a big turret, but had a 152 mm HE gun, which was more powerful than artillery of the same perioid. The T-150 had the less-powerful 107 mm ZiS-6 gun (this one can also be mounted on the KV-2), with better DPM and aiming characteristics than the KV-1S' gun, but a worse damage output.
The original KV chassis used on heavy tanks stopped in the development of the KV-1S. After the KV-1S the IS series was born, featuring the original IS, with a better version of the KV-1S' 122 mm gun, the IS-3, with the legendary BL-9 gun, the IS-8, with the 122 mm M62-T2 gun, and the pinnacle, the IS-7, the biggest heavy tank of the USSR. The S-70 gun was very powerful, which makes it a good heavy tank.
The development of the KV chassis did continue into the KV-3, KV-4, and KV-5, and even in the medium KV-13. But the chassis was better armored and bigger for the heavy KV's, having to stand a lot of shots from the enemies.
In World of Tanks the KV-1S, T-150, and KV-2 are the choice of 3 tier VI heavy tanks.
The development didn't stop here. The SU tank destroyer series was developed on the chassis of the T-70 light tank, and later on the T-34 medium tank. The T-70 chassis was used on the SU-76 and SU-85B, the T-34 chassis was used on the SU-85, and SU-100. Then, for the new TD, the SU-152, featuring the dangerous 152 mm ML-20 cannon, which was a development for the ISU-152 and Object 704's 152 mm BL-10 cannon, they used the KV chassis to power the SU-152 and ISU-152. The armor didn't do that good, because the reason the KV-3, 4 and 5 were equipped with better armored KV chassis was because of the more powerful guns shooting back. The SU-152 was used very long though.
And then, they even used the KV-2's chassis for the S-51 artillery. This is the top of open-topped artillery, being a chassis with a gun, and that's it. The reason is because of the monstrosity of the 203 mm cannon fitted to it. The S-51 was the only artillery with the KV chassis. After the S-51, the SU-14 chassis was used, for the SU-14 Mk. II.