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.

The Haubitze M1 was best described as an enlarged 24 cm Kanone 3. It used many of the same design principles as the smaller weapon including the dual-recoil system and a two-part carriage capable of all-around traverse when mounted on its firing platform. It also disassembled into six loads for transport. The loads were cradle, barrel, top carriage, bottom carriage, front platform and turntable and the rear platform. Each piece on its trailer was towed by a 18 t  Sd.Kfz. 9 half-track. A seventh half-track towed the gantry crane required to assemble the weapon. The gantry crane (powered by a generator on its towing vehicle) would be erected at the new firing position and would take about two hours to assemble the entire weapon.