Because, even in a 'hot' conflict, Colonial Marine units are often dispersed in small units across continental distances, the USCM logistic prime movers are the ubiquitous UD-4 Cheyenne dropship and the CS-14 Briareos heavy lift shuttle. In the field, the M570 all-terrain transport is the land based prime mover, with powerloaders often used on-site to offload cargoes. - Aliens: Colonial Marines Technical Manual