In 1960, the U. S. Army requested proposals for the LOH program, a small, maneuverable, personnel transport, cargo, MedEvac, light ground attack, artillery, and photo reconnaissance helicopter. The LOH program was won by the Hughes (model 369) YOH-6A Cayuse. Though not selected, the Bell (model 206) YOH-4A (1961), powered by an Allison T63-A-5 250 shp turbine engine, evolved into the successful Bell (model 206A) Jet Ranger. When the LOH program was reopened for an additional buy in March 1968, the Army selected the Bell model 206A, which was type classified as the OH-58A Kiowa light observation helicopter.

The Boeing (McDonnell Douglas - formerly Hughes model 369A) OH-6A was designed for use as a military scout during the Vietnam war to meet the U. S. Army's need for an extremely maneuverable light observation helicopter (LOH). Initially fielded in Vietnam in early 1968, the Hughes OH-6A was used for command and control, observation, target acquisition, and reconnaissance. The Cayuse was organic to division, brigade, and battalion size units. The four-passenger tear-drop shaped "Flying egg" (six-passengers with rear seats folded down) was a small, light, sturdy, maneuverable helicopter, with very low drag.

The OH-6A Cayuse was quite effective when teamed with the AH-1G Cobra attack helicopter as part of what were known as "Pink Teams". The OH-6A "Loach" (for "LOH") would find targets by flying low, "trolling for fire", then marking the target with colored smoke to lead in a Cobra, or "Snake", to attack. The Cayuse could absorb an extensive amount of small arms fire and still bring the crew home safely. The OH-6A could be armed with the M27 armament subsystem, the port (left) side mounting M134 six-barrel 7.62mm "Minigun" or a 40mm grenade launcher on the XM8 armament subsystem. In addition, an M60D 7.62mm machine gun could be mounted in the rear starboard (right) door opening. The OH-6A replaced the Korean era OH-13 Sioux and OH-23 Raven light observation helicopters. The Cayuse had a single articulated four-bladed main rotor, a metal two-bladed tail rotor, and a V-shaped tail. The OH-6A was powered by a single Allison T63-A-5A 285 shp turboshaft engine, and had a cruising speed of 144 mph (125 knots).