M1931 (B-4) 203mm Howitzer WWII

The Soviet B-4 high power heavy howitzer with a calibre of 203.2 mm (8 in) was developed in 1931.
The howitzer could fire shells weighing more than 100 kg at a range of almost 18 km. The weight of the gun was 19 t in transport position. A special caterpillar carriage was developed - a large tracked bearing surface prevented the howitzer from sinking into the ground, and the strong carriage withstood the powerful recoil when firing.

The first combat use of the B-4 took place during the Soviet-Finnish War of 1939-40, when it was used to destroy Finnish concrete fortifications. The Finns nicknamed the gun "Stalin's Sledgehammer". The German Army captured a number of these guns and used them under the designation 20,3 cm H.503 (r). The howitzer was used throughout WWII. 

The gun was successfully used in storming fortresses and in battles in the streets of large German cities.