The Panzerkampfwagen VIII Maus was one such weapon. It was impractical and also huge — so huge it holds the record for the heaviest fully-enclosed tank ever built. The Maus weighed 180 metric tons.

It also did not have a traditional tank gun. Instead, the Maus packed a 15-centimeter howitzer specifically on Hitler’s orders. Although only one of the two prototypes ever produced had a turret.