The Allis-Chalmers M7 snow tractor was designed for use by the U.S. Army Air Corps as a rescue vehicle in remote northern bases.
The M7 (T26E4) snow tractor was standardized in August 1943, and was downgraded to Limited standard in November 1944. It was intended to pull a one-ton M19 snow trailer (T48). The tractor used many Allis Chalmers farm tractor components. It also used many MB jeep powertrain components to lessen the military's spare parts inventory requirements.
The distinguishing feature of the M7 was the track system (halftrack). The M7’s track ran on two rubber belts with four steel cables inside. The machine had a tendency to have the tracks come off in use. Another feature of both the tractor and trailer is that the tires could be switched with skis.
Prototyping of the machine that eventually became the M7 included several machines by Emmett Tucker ( of subsequent Tucker Sno-Cat fame ) At least one of the prototypes, a T26E3, still exists.
Something over ten percent of production, over 30 units, still survive. The track system and track plate width (18") look to have been borrowed from the early versions of the Weasel, although the M7 tracks are shorter with fewer plates.