The Hughes OH-6 Cayuse (nicknamed “Loach”) is a single-engine light helicopter with a four-bladed main rotor used for personnel transport, escort and attack missions, and observation. Hughes Helicopters also developed the Model 369 as a civilian helicopter, the Hughes Model 500, currently produced by MD Helicopters as the MD 500.

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In 1960, the United States Army issued Technical Specification 153 for a Light Observation Helicopter (LOH) capable of fulfilling various roles: personnel transport, escort and attack missions, casualty evacuation and observation. Twelve companies took part in the competition and Hughes Tool Company's Aircraft Division submitted the Model 369. Two designs, those submitted by Fairchild-Hiller and Bell, were selected as finalists by the Army-Navy design competition board, but the U.S. Army later included the helicopter from Hughes as well.

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The first Model 369 prototype flew on 27 February 1963. The helicopter entered service in 1966, arriving in the Vietnam War thereafter. The pilots dubbed the new helicopter Loach, a word created by pronunciation of the acronym of the program that spawned the aircraft, LOH (light observation helicopter).

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The OH-6 set 23 world records for helicopters in 1966 for speed, endurance and time to climb. On 26 March 1966, Jack Schwiebold set the closed circuit distance record in a YOH-6A at Edwards Air Force Base, California. He flew without landing for 1,739.96 mi (2,800.20 km). Subsequently, on 6 April 1966, Robert Ferry set the long distance world record for helicopters. He flew from Culver City, California, with over a ton of fuel to Ormond Beach, Florida, covering a total of 1,923.08 nm (2,213.04 mi, 3,561.55 km) in 15 hours, and near the finish at up to 24,000 feet altitude. As of 2013, these records still stand.

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A heavily modified pair of OH-6As were utilized by the CIA via Air America for a covert wire-tapping mission in 1972. The aircraft, dubbed 500P (penetrator) by Hughes, began as an ARPA project, codenamed "Mainstreet", in 1968. Deployed to a secret base in southern Laos (PS-44) in June 1972, one of the helicopters was heavily damaged during a training mission late in the summer. The remaining helicopter deployed a wiretap near Vinh, Vietnam on the night of 5–6 December 1972, which provided the United States with useful information during the Linebacker II campaign and Paris Peace Talks. Shortly thereafter, the aircraft were returned to the U.S., dismantled and quietly found new homes as the now-standard 500s. 842 out of the 1,419 OH-6As built for the US Army were destroyed in Vietnam, mostly from hostile ground fire.​