After demonstrating the ability/ design of the K-225 to the US Navy and Coast Guard (the Navy bought two and the Coast Guard one) and the benefit of the synchropter design, Kaman was awarded a contract in 1950 to design a completely new helicopter for the Navy. Designated the HOK-1 the helicopter was to be designed to strict military requirements. The initial contract was to produce four test aircraft to fill the US Marine Corps requirement for an Observation Helicopter. The first flight took place on 21 April 1953 and production continued until 1958.

P.Allen "The Helicopter", 1996

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