Frank N. Piasecki formed company 1941 as PV Engineering Forum, incorporated in Pennsylvania 1943, making parts for PBY and for radars. Increasing design effort devoted to single-seat experimental helicopter, PV-2 (11 April 1943), leading to various NACA contracts and award of Helicopter Pilot Certificate No. 1 to Mr P. In February 1944 Navy contract for large transport helicopter led to PV-3 (8 March 1945) with banana-like fuselage with 41-ft (12.5 m) rotor at each end. This led to production HRP Rescuers, and restructuring as Piasecki Helicopter Corp. with large plant at Morton, Philadelphia, September 1946. HRP led to PD-22, Army H-21, Navy HRP-2, redesigned smooth metal fuselage, 554 being produced by 1959. Smaller PV-14, again tandem-rotor, led to over 400 HUP Retriever and H-25 Army Mule. In May 1955 'as result of bitter managerial disagreement Mr Piasecki was relieved of his positions' and with many associates resigned and formed a new company (see Piasecki Aircraft Corp.). Original had to be renamed, becoming Vertol in March 1956.