In the early 1960s, the U. S. Army began a search for a turbine-powered Light Observation Helicopter (LOH) to replace the piston-engined Bell OH-13s. Several companies provided bids for the prototype, but Hughes Aircraft won the contract with the Model 369, which became the OH-6 Cayuse. First flown on February 27, 1963, the agile little aircraft with the three-finned tail was soon being called the “Loach” by U. S. soldiers. The unique teardrop-shaped fuselage earned the OH-6 the sobriquet “Flying Egg,” but the shape and internal bulkheads provided an exceptionally crashworthy aircraft, especially after Hughes installed self-sealing, crash-resistant fuel tanks to prevent post-crash fires.
The large Plexiglas windscreen offered the pilot excellent visibility, and the four-bladed fully articulated rotor system provided much more maneuverability than the semi-rigid rotor of the OH-13. The Allison T63-A-5A 250 turbine produced 317 horsepower, giving the OH-6 more speed, 130 knots, and allowed the aircraft to carry up to five passengers, or 1,000 pounds of internal cargo. In 1966 the OH- 6 set the first of its twenty-three international records by covering 1,923 nautical miles in a single straight-line flight. In 1967 the Loach first appeared in Vietnam performing such duties as command and control, liaison, fire direction, light utility, and reconnaissance. In the air cavalry role, the crew usually consisted of a pilot and observer; the helicopter was fitted with an M-27 7.62-mm minigun system, and the observer was armed with an M-60 machine gun. The Army eventually ordered 1,420 OH-6s, which were delivered between 1966 and 1970.
The OH-6 proved so effective that the Japanese Self-Defense Force let a contract with Kawasaki Heavy Industries to produce a version of the helicopter. KHI built the export version of the OH-6, the Hughes 500M Defender, designated the OH-6J in Japan. KHI produced a later version with a larger five-bladed rotor system designated the OH-6D. The Japanese military purchased 120 OH-6Js and 62 OH-6Ds. Kawasaki also marketed the 369HS and 369D for EMS, police, and agricultural services.