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.