The 35.5 cm Haubitze M1 was a German siege howitzer. It was developed by Rheinmetall before World War II to meet the German Army's request for a super-heavy howitzer. Eight were produced between 1939 and 1944. It saw service in the Battle of France and spent the rest of the war on the Eastern Front, saw action in Operation Barbarossa, the siege of Sevastopol, the siege of Leningrad and helped to put down the Warsaw Uprising in 1944.