As Aussie Jeepster posts, Motor Transport is the generic name for the unit on base that holds pool vehicles, cars, station wagons, small and large buses and occasionally something 4WD. When I was involved it was more usual for 4WDs, trucks and specialist vehicles to be held by units who required them.
MT have their own shed and a yard with washing and fuelling facilities nearby.
It was (and I hope still is) considered polite to wash and fuel the vehicle before it was returned to MT at the end of the day (or longer approved borrowing period).