The 15 cm sIG 33 (Sf) auf Panzerkampfwagen I Ausf B, sometimes referred to (unofficially) as the Sturmpanzer I Bison, was a German self-propelled gun used during World War II.

Plates 13 mm (0.51 in) thick were used to form a tall, open-topped fighting compartment on the forward part of the hull.

This protected little more than the gun and the gunner himself from small arms fire and shell fragments, the loaders being completely exposed.

("self-propelled heavy infantry gun companies") numbers 701–706, assigned to Panzer divisions in the Battle of France[2] as follows:[3] As part of the 5th Panzer Division, assigned to the German XIVth Motorized Army Corps, the 704th company participated in Operation Marita, the invasion of the Balkans.

[citation needed] Of the remaining companies, only the 701st participated in the opening stages of the subsequent Case Blue in 1942, although it, and its parent 9th Panzer Division, were transferred to Army Group Center by the end of the summer of 1942.