Aviation played a major role in the United States Army and was organic to most large combat formations rather than organized as a separate branch of the service. During the Vietnam war US Army helicopters, plus a smaller number of fixed-wing aircraft, were used in greater numbers and in more diverse tasks than had ever been seen before in a land war. In fact, US Army aviation had to expand so dramatically that it became, entirely on its own account, the world's third-largest air force.
Helicopters used by the US Army were generally classified under five main types:
Sometimes these classifications were changed for a helicopter that was converted to do another task, such as the CH-47 Chinook Gunship which was reclassified ACH-47, 'Armored Cargo Helicopter'. This was not always the case though as with the Huey gunships which retained their original classification, UH-1, rather than becoming AUH-1 or 'Attack Utility Helicopter' for instance.
It was largely because of the Vietnam war that one helicopter in particular, the Bell UH-1 'Huey', became the second most numerous aircraft since World War 2. It provided the backbone not only of US Army airmobility in Vietnam but also, in the later of its many versions, its aerial firepower in the form of 'Hogs' or Gunships. There was no significant clash of arms on the soil of South Vietnam in which the UH-1 did not participate and at the end of the US involvement the number of these helicopters left behind in RVN exceeded the entire helicopter strength of any air force in Western Europe at that time.
Two much larger helicopters were used for heavy lifts. The more common was the Boeing Vertol CH-47 Chinook, a large tandem-rotor transport with a fuselage able to seat 44 equipped troops or carry modest vehicles and artillery. Only the earlier CH-47A and B models were in use in the initial Vietnam conflict, with maximum payload of about 15,000 lb (6804 kg). From September 1968 these were augmented by the CH-47C, with much more powerful engines and a payload of over 23,000 lb (10433 kg) in the voluminous cabin or 28,000 lb (12701 kg) on an external hook. Chinooks could fly in as slung loads all the air-portable guns, ammunition and supply packages used in Vietnam, as well as such mundane items as trucks of drinking water. Chinooks eventually replaced the the CH-37 "Mojave" as the primary aircraft recovery helicopter. In this role they are reputed to have picked up and brought back more than 11,000 downed aircraft - worth a reported $2,990 million - in what were called 'pipe smoke' missions.
Even more powerful, but used in much smaller numbers, the Sikorsky CH-54 'Tarhe" remains the only large crane helicopter in the Western world. Most of the Tarhes in US Army service saw combat duty in Vietnam, carrying as slung loads bulldozers, graders and light armour, picking up and repositioning artillery and also rescuing over 380 downed aircraft.
Among secondary US Army types in Vietnam were small numbers of older helicopters including the Bell OH-13 "Sioux" and OH-23 "Raven" observation helicopters, the Vertol CH-21 "Shawnee" and Sikorsky CH-34 "Choctow" (designated the UH-34 "Dog" by USMC) , and the much newer Bell OH-58A Kiowa.
Air Cavalry - composition and employment of an Air Cavalry Troop
D Troop 3/5th Air Cavalry - commentary on the role and organisation of an actual Air Cavalry Troop