03 mm howitzer M1931 (B-4) was a 203 mm Soviet high-power heavy howitzer. During the Second World War, it was under the command of the Stavka's strategic reserve. It was nicknamed "Stalin's sledgehammer" by German soldiers. These guns were used with success against Finnish pillboxes at the Mannerheim Line, heavy German fortifications and in urban combat for destroying protected buildings and bunkers. These guns were used until the end of the war in the Battle of Berlin, during which the Red Army used them to smash German fortifications at point blank range with their heavy 203mm shells. In the spring of 1944, a KV-1S tank chassis was used to create a self-propelled variant, the S-51. The heavy recoil from the muzzle blast threw the crew off their seats and damaged the transmission, and so it was cancelled.
