KV-2

The KV-2 was a 1940 tank designed to blow up Mannerheim Line fortifications by putting a new turret with 152 mm howitzer on KV-1 chassis. Notice that it's not the amazing gun from ISU-152, but older M-10 howitzer with shorter barrel (poorly suited for direct fire) and slightly worse ammunition. During the Winter War, the Soviet army was semi-disabled from recent purges and barely understood what they were doing, so it's hard to judge the performance of the tank itself.

However it's problems became well known. The transmission was very prone to breaking, the gun wasn't properly centered so the turret couldn't rotate if you tilt it by parking the tank on a slope and shooting while moving could dislocate the turret. The tall, slow tank that had to shoot while staying still was an easy target. Don't forget T-34-tier navigation tools.

A year later, just like the KV-1, the tank was almost invulnerable to German early war AT weapons except 88 mm Flaks. Random types of ammunition like shrapnel and anti-concrete were often used due to shortages. In the end, almost all of 204 KV-2 tanks were lost in 1941.

As silly and excessive the project was, if that 152 mm explosive somehow managed to hit any tank it instantly killed the crew and dislocated the turret often outright sending it flying. KV STRONK!