A right side view of a CH-46 Sea Knight helicopter from Marine Medium Helicopter Squadron 365 (HMM-365), during a troop lift between the Main Side Landing Zone and the Operations Landing Zone

Known as the "Phrog", the Sea Knight was used in all U.S. Marine operational environments between its introduction during the Vietnam War. The type's longevity and reputation for reliability led to mantras such as "phrogs phorever" and "never trust a helicopter under 30". During the 1940s and 1950s, American rotorcraft manufacturer Piasecki Helicopter emerged as a pioneering developer of tandem-rotor helicopters; perhaps the most famous of these being the piston-powered H-21 "Flying Banana", an early utility and transport helicopter. During 1955, Piasecki was officially renamed as Vertol Corporation (standing for vertical take-off and landing); it was around this time that work commenced on the development of a new generation of tandem rotor helicopter. During 1956, the new design received the internal company designation of Vertol Model 107, or simply V-107; this rotorcraft differed from its predecessors by harnessing the newly developed turboshaft engine instead of piston-based counterparts. In 1960, American Boeing acquired Vertol and in 1961, it was announced that Boeing Vertol had been selected to manufacture its model 107M for the U.S. Marine Corps. Following the Sea Knight's first flight in August 1962, the military designation was changed to CH-46A.