UH-1A – 173 produced. Twenty were sent to Vietnam in 1962 for tests in various roles, troop transport, aeromedical evacuation, and armed helicopter escort. It proved underpowered for the last. Even so, they were so superior to the piston engine types in use that the Army decided to replace all previous types with UH-1s.
UH-1B – First major production version, 1033 built. Engine upgrade from 860 SHP to 960 SHP. Cabin slightly enlarged. Some were sent to Vietnam in 1962 and there were 250 in-country in 1964. On their replacement by newer models, some were passed to the South Vietnamese Air Force and a few to the US Navy. The Navy operated them as armed helicopters under its SEAWOLF program to support the SEALs and Riverine Force in the Mekong Delta.
The helicopter was also built under license in several countries and served in Vietnam with the Royal Australian Air Force contingent supporting their forces.
(Replaced by the US Army, some were retained for special tests. Three UH-1Bs were in Vietnam in 1972, to test the new TOW anti-tank guided missile. When the North Vietnamese launched their Easter Offensive, the three were sent into combat. Their rockets devastated the NVA tank columns, and they played a major role in several key battles.)
UH-1C – The Army had requested a specialized attack helicopter (later the AH-1G), but as an interim measure took 750 UH-1Cs in this role. This was the UH-1B engine and airframe, but used the drivetrain and rotor system developed for the AH-1G attack helicopter. It mounted a huge variety of machineguns and rocket packs, in different configurations. Extremely efficient in its role as a gunship, it served through the end of the war. Some had an engine upgrade to 1400 SHP in 1969 and were redesigned UH-1M.
UH-1D – This was a major production version, with 2008 being produced. It was used as a troop transport “slick” and for Medevac. Engine upgrade to 1100 SHP, and a still larger cabin. Some were eventually upgraded to H’s.
UH-1E – A UH-1B for the Marine Corps. Changes were to an aluminum airframe, to resist salt water corrosion (other UH-1s are magnesium) and Navy/Marine avionics. The Marines armed these as gunships in Vietnam. 209 produced.
UH-1F – UH-1B for the US Air Force. Engine upgrade to 1272 SHP (to use a common engine with another USAF helicopter.) The Air Force used them as VIP transports and to support their Security Police teams guarding missile silos in the US. They did arm some as gunships, and used them in Vietnam.
AH-1G – The two seat Hueycobra attack helicopter. It shared only minor parts with any of the other versions.
UH-1H – still another engine upgrade (to 1400 SHP) and with additional all-weather flying instrumentation added. The major production version, 3,573 were produced for the US Army alone, supplemented by additional conversions from UH-1Ds. A further 1,372 were produced for foreign sales, and it was also produced under license abroad. In Vietnam, some were armed as gunships to replace UH-1Cs and the type was only retired completely from the US military around 2000. TOD had this version of the Huey. And one wreck.
All other Huey versions are post Vietnam, or non-combat (trainers for the US Navy, for example).