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.

It also used many Willys MB jeep powertrain components to lessen the military's spare parts inventory requirements.

It had a wooden body on a steel hollow-section frame, with hood, hoops, side and end panels all easily detachable, and it was normally equipped with a heater and two stretchers, plus a rear pintle hitch so that trailers could be doubled up.

The two-bolt mounting pintle hitch was unique to the M7 and M19, and would not accommodate even an ordinary MB / GPW jeep trailer lunette.

They had three main functions; Rescue and recovery, for which they were equipped with two stretchers and a personnel heater Aircraft starting, for which they were outfitted with much larger aircraft engine heaters and slave power equipment Cargo, for which they could be operated with or without canvas hood, top bows, side and end frames Serial numbers for the 1950 units seem to start at 1,000 and were dated around November of that year, suggesting they were made to supplement a batch of 1944 originals that were going to Norway, and seem to top out around 1,150.

The 1944 originals had several noted weak points which can all be attributed to the lightness of construction ( they were rated at 2,000 lbs, same as a Ben Hur trailer, but weighed only one third as much - 640 lbs ) The 1944 tow bar frames had holes for bolting through the drag chains - 1950 trailers had no holes and drag chain ends welded to the tow frame.