The H-21 was the fourth tandem rotor helicopter design to come from Piasecki. It was first flown in 1949 and was used by the U.S. Army, U.S. Air Force, Canadian Air Force, French Navy, and West German Air Force. The CH-21C was used as an assault transport during the early years of American involvement in the Vietnam War. It could carry 20 troops at a time but was considered very vulnerable to ground fire. It was the primary helicopter used in Vietnam until 1964 when the Army began to replace it with UH-1 and CH-47.
93rd Transportation Company, South Vietnam, 1962
Pima Air & Space Museum