The M4 was a heavy tractor based on the chassis of the M2 Light Tank manufactured by Allis-Chalmers for towing heavy artillery pieces. The guns that the M4 towed, such as the M1 Field Gun, were almost completely dependent on the M4 tractor for both ammunition and transport. The M4 was also capable of of transporting the gun's crew and other cargo in its rear storage space. The frontal crew cabin had room for two individuals.
The M4 had a gasoline powered 210 hp Waukesha 145GZ engine capable of propelling it at speeds of up to 56.3 km/h (35 mph). The tractor's only armament was a single Browning M2HB mounted on top of the cabin. The ring mount where the Browning was mounted was accessed via a hatch above the main body. The M4 featured no armor protection for its crew or its passengers.
The M4 also had a vertical volute suspension system for better traction and mobility. Its maximum operating range of the M4 was 289.6 km.
The original purpose of the M4 High-Speed Tractor was the need for a vehicle that could tow heavier artillery guns and anti-aircraft guns, such as the 155mm M1 "Long Tom".
After its production began, the M4 High-Speed Tractor started its service in 1942 and was used by American forces until about 1960. It was used in European Theater, assigned to numerous artillery units. The M4 was also shipped internationally after World War II, a number arriving in Yugoslavia and Japan.
From 1943 to 1946 about 5,000 had been produced. 
The M4 High Speed Tractor's only variants were the M4C which had special ammunition storage in the crew area and the M4A1 which had a modified suspension system which became wider than the original vehicle.
There were also some unredesignated variants that were meant for towing different types of artillery. For example, one variant was meant for towing anti-aircraft guns and the other was meant for howitzers. Some models even had a crane in the back to hoist heavier ammunition.
- ↑ http://ww2db.com/vehicle_spec.php?q=263
- ↑ http://olive-drab.com/idphoto/id_photos_m4_hst.php
- ↑ Lüdeke, Alexander. Weapons of World War II. Parragon Books Ltd. (2007), Page 58