The K-225 is an experimental intermeshing rotors helicopter developed by Kaman Aircraft and built at the company's original factory at KBDL. The success of the concept led to the development of the HTK-1 and HOK-1 and eventually the HS-43 Huskie. This example was the fifth helicopter built by Kaman and the company's oldest surviving aircraft.

Just delivered to the USN for testing. 125477 became the first turbine-powered helicopter in 1951. Photo from: National Museum of the US Navy

The K-225 was intended as a cropduster but two examples were delivered to the US Navy, one to the Coast Guard, and one to the USAF as the YH-22. USCG 239 later became 1239. Little used after initial testing. Transferred to US Navy in 1954. Sold off and reported destroyed in a crash on 1 October 1955. Photo from: National Museum of the US Navy

A Kaman K-225 was re-engined with a Boeing YT50 turboshaft to become the first turbine-engined helicopter to fly on 11 December 1951. Photo is said to show the maiden flight. The helicopter was owned by the USN but got no military designation. Photo from: Nederlands Instituut voor Militaire Historie

The K-225 was an improved version of Charles Kaman's first helicopter, the twin inter-meshing rotor K-125 and first flew in 1949. Two were purchased by the US Navy and one by the US Coast Guard for testing. One was also evaluated by the US Air Force. 125477 became the first turbine-powered helicopter in 1951 when the Lycoming piston engine was replaced by a Boeing YT-50 turboshaft engine. The helicopter was donated to the Smithsonian in 1957.

1949-built twin-seat experimental helicopter design with twin intermeshing rotor blades. This was the fifth of seven completed and was retained by Kaman for development work. The US Navy and Coast Guard tested a few in the early 1950s.