The HU-1A (later redesignated UH-1A) first entered service with the 101st Airborne Division at Fort Campbell, Kentucky, the 82nd Airborne Division, and the 57th Medical Detachment. Although intended for evaluation only, the Army quickly pressed the new helicopter into operational service and Hueys with the 57th Medical Detachment arrived in Vietnam in March 1962.
The UH-1 has long been a symbol of US involvement in Southeast Asia in general and Vietnam in particular, and as a result of that conflict, has become one of the world's most recognized helicopters. In Vietnam primary missions included general support, air assault, cargo transport, aeromedical evacuation, search and rescue, electronic warfare, and later, ground attack. During the conflict, the craft was upgraded, notably to a larger version based on the Model 205. This version was initially designated the UH-1D and flew operationally from 1963.
During service in the Vietnam War, the UH-1 was used for various purposes and various terms for each task abounded. UH-1s tasked with a ground attack or armed escort role were outfitted with rocket launchers, grenade launchers, and machine guns. As early as 1962, UH-1s were modified locally by the companies themselves, who fabricated their own mounting systems. These gunship UH-1s were commonly referred to as "Frogs" or "Hogs" if they carried rockets, and "Cobras" or simply "Guns" if they had guns. UH-1s tasked and configured for troop transport were often called "Slicks" due to an absence of weapons pods. Slicks did have door gunners, but were generally employed in the troop transport and medevac roles.
UH-1s also flew hunter-killer teams with observation helicopters, namely the Bell OH-58A Kiowa and the Hughes OH-6 Cayuse (Loach). Towards the end of the conflict, the UH-1 was tested with TOW missiles, and two UH-1B helicopters equipped with the XM26 Armament Subsystem were deployed to help counter the 1972 Easter Invasion.
During the course of the war, the UH-1 went through several upgrades. The UH-1A, B, and C models (short fuselage, Bell 204) and the UH-1D and H models (stretched-fuselage, Bell 205) each had improved performance and load-carrying capabilities. The UH-1B and C performed the gunship, and some of the transport, duties in the early years of the Vietnam War. UH-1B/C gunships were replaced by the new AH-1 Cobra attack helicopter from 1967 to late 1968. The increasing intensity and sophistication of NVA anti-aircraft defenses made continued use of UH-1 gunships impractical, and after Vietnam the Cobra was adopted as the Army's main attack helicopter. Devotees of the UH-1 in the gunship role cite its ability to act as an impromptu dustoff if the need arose, as well as the superior observational capabilities of the larger Huey cockpit, which allowed return fire from door gunners to the rear and sides of the aircraft.
During the war 7,013 UH-1s served in Vietnam and of these 3,305 were destroyed. In total 1,074 Huey pilots were killed, along with 1,103 other crew members.
The US Army phased out the UH-1 with the introduction of the UH-60 Black Hawk, although the Army UH-1 Residual Fleet had around 700 UH-1s that were to be retained until 2015, primarily in support of Army Aviation training at Fort Rucker and in selected Army National Guard units. Army support for the craft was intended to end in 2004. The UH-1 Huey was retired from active Army service in 2005. In 2009, Army National Guard retirements of the UH-1 accelerated with the introduction of the UH-72 Lakota.