The M113 is operated by US and ARVN forces in Battlefield Vietnam. It can seat up to six people: 1 driver, 1 gunner and 4 passengers. It's amphibious and well armored but the gunner and driver are exposed, and its only armament is a single M2 Browning machine gun which overheats after extended firing.
The M113's real gift is the fact that the four passengers in the back are not only completely protected, but they also have access to unlimited ammunition and medical supplies. It should usually be kept slightly back out of large battles or choke point battles, but in a place where access is easy for wounded soldiers.