It gained impetus with the advent of the Vietnam War, and was aided by advances in helicopter technology, specifically the development of the turboshaft engine.

On 11 October 1955, CONARC recommended that the Department of the Army initiate a program to develop a replacement observation helicopter for the aging OH-13 Sioux and OH-23 Raven.

[3] On 14 October 1960, the United States Navy Bureau of Weapons issued Technical Specification 153, a request for proposals (RFP) for a four-seat, turbine-powered, light observation helicopter capable of fulfilling various roles: personnel transport, escort and attack missions, casualty evacuation and observation.

[3][5] The United States Navy provided technical expertise to assist the Army in evaluating the design proposals.

As a result of the flight evaluation, Hiller's YOH-5 and Hughes' YOH-6 were selected to compete in a program cost analysis bid for the contract.