A C-7 Caribou aircraft, transferred from the U.S. Army to the Air Force on Jan. 1, is used for airlifting supplies to forward outposts in Vietnam. With a maximum payload of three tons, the C-7A can take off and clear a 50-foot obstacle in about 1,200 feet. The aircraft, used for landing at short, unimproved airfields, can land on a 1,000-foot runway