203 mm howitzer M1931 (B-4) was a 203 mm (8 inch) 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.

The SU-14 was a prototype Soviet heavy self-propelled gun that started out as an open topped vehicle, with the armor being added later on when it was converted into a direct-fire assault gun in 1941. The original prototype, using a modified T-28 chassis, mounted a 203 mm gun B-4 and by 1937 a 150 mm naval gun B-30; the SU-14-1 variant of 1936, using a T-35 chassis, mounted the 203 mm gun B-4 and later the 152 mm gun M1935 (Br-2). Both versions never entered serial production.