The M4 Mortar Carrier Halftrack was based on the M2 Halftrack, with modifications to carry the 81mm mortar and its crew.
A mobile mortar, mounted in the half-track vehicle, has excellent cross-country mobility and, under most conditions of terrain, can follow tanks and other vehicles without loss of distance. It may be moved rapidly into position and fired either from the vehicle or the ground. In field experience, the mortar was usually fired from the halftrack.
Firing the 81mm mortar from inside the M4 Mortar Carrier Halftrack.
The M4 Mortar Carrier Halftrack was produced by White Motor Company for a period of about one year during 1941-1942. Total production was 572 units. The M2 halftrack side stowage areas were used on the M4 halftrack to hold 28 mortar rounds in addition to 68 rounds carried in the crew compartment (96 total).
The mortar was carried facing the rear of the halftrack. A square steel door in the rear wall of the M4 halftrack was used to deploy the mortar for firing, but it was difficult to do since the machine gun skate rail ran across the door area. Experience with the M4 Mortar Carrier Halftrack indicated that it was impractical to deploy the mortar, so the vehicle was redesigned to allow the mortar to be fired from an expanded and strengthened position in the crew compartment. During 1943, about 600 additional vehicles were produced by White with the new design. Existing M4 halftracks were upgraded to the new configuration. Both new production and retrofitted vehicles were known as the M4A1 Mortar Carrier Halftrack.
A further upgrade replaced the M2 Halftrack with the M3 Halftrack as the base vehicle, redesignated as the M21 Halftrack Mortar Carrier. The main innovation was to have the mortar face forward, making it even easier to move to a new position and fire immediately.
2nd Armored Division M4 Halftrack 81mm Mortar Carrier, April 1942.
M4A1 Halftrack 81mm Mortar Carrier, near Overloon, Holland, October 1944.
M-4A1 Halftrack Mortar Carrier. Photo: Courtesy of John Buckley.