With the US Navy requiring a new patrol flying-boat, Martin decided to develop the successful PBM Mariner, the resulting Martin Model 237 design combining the wing and upper hull of the Mariner with the new lower hull structure. The close relationship between the two types is emphasised by the fact that a PBM-5 Mariner served as the prototype XP5M-1 which, when ordered into production, was given the name Marlin. The modified hull of the XP5M-1 incorporated radar-directed nose and tail turrets, as well as a power-operated dorsal turret, and power was provided by two 2424kW Wright R-3350 radial engines. This prototype flew for the first time on 30 May 1948, but it was not until two years later that the P5M-1 was ordered into production, the first of these series aircraft being flown on 22 June 1951. Initial deliveries, to US Navy Squadron VP-44, began on 23 April 1952 and the type remained in service until the mid-1960s. In addition to those operated by the US Navy, 10 of the later P5M-2 version were supplied to France under the American MAP for use by the Aeronavale.