In 1957, Lockheed proposed a new design (based on the L188 Electra airliner) to replace the United States Navy’s ageing fleet of P2V Neptune and P5M Marlins. The proposal met all of the navy’s requirements and was accepted in April 1958. A prototype was created from a modified Electra and designated YP3V-I and flew on 25 November 1959. This would later be designated the P-3A Orion. By late 1960 a production contract was in place and the first P-3A flew in April 1961, entering service with the United States Navy August 1962.