Comparing: Sturmpanzer I Bison vs. T18 HMC

Developed from 1939 through 1940 on the chassis of the Panzerkampfwagen I. Equipped with the 150 mm s.I.G. 33 gun that was mounted together with the gun carriage. Rate of fire was three rounds per minute; on-board ammunition totaled eight shells. The vehicle required the support of an ammunition carrier. The SPG was used from 1940 through 1943 during the French Campaign, Balkan Campaign, and on the Eastern Front. Later the Sturmpanzer II with a similar gun type was developed.

A proposed 75 mm howitzer on the chassis of the M3 light tank. Developed by the Firestone Tire and Rubber Company in the fall of 1941. Two prototypes were ordered after the project was approved. The first vehicle was produced in May and underwent trials in June 1942 on the Aberdeen Proving Ground. The project was discontinued in favor of more promising designs.