The OH-23 Raven (also known by its company designation UH-12) was designed by Stanley Hiller Jr (a engineer prodigy who built his first helicopter at the age of 18) from the civilian Model 360, the first helicopter to make a transcontinental commercial flight. It was subsequently adopted by the US Army as an observation platform and for battlefield evacuation in which case it could carry two stretchers in external panniers. It was also used by the US Navy as a trainer. The OH-23 was fitted with either skids or tricycle landing gear, and also featured the company's distinctive Rotor-Matic control system. Over two thousand military and civilian versions were built and were exported to numerous countries, particularly Latin American ones, as well as NATO allies Canada, Netherlands and the UK (Royal Navy). A number were in use as scouts during the Vietnam War but these were eventually replaced by the OH-6. Of those used in Vietnam, some were armed with one or two machine guns.

Based on the commercial Model 360, the first prototype YH-23 was evaluated by the US Army in 1948 and entered service as the H-23A. Upgraded engines were fitted on the H-23B while the H-23C had a three-seat cabin and a distinctive "goldfish bowl" canopy. A new rotor, transmission and engine was installed on the H-23D after which the four-seat H-23F followed and a three-seat dual control version, the H-23G, which was the most widely produced variant. Versions for other services included the HTE-1 and HTE-2 for the US Navy, the Hiller MT Mk 1 and Mk 2 for the Royal Navy and the Canadian CH-112 Nomad. After 1962, all US versions were redesignated OH-23