The Marlin was designed as a gull-winged aircraft to place the engines and propellers high above the spray. Power was by two Wright R-3350 radial engines. The rear hull did not lift sharply from the water at the tail, instead rising up steadily, a Martin innovation; this gave the aircraft a longer base of flotation and reduced "porpoising" over waves.

The prototype had nose and tail turrets with twin 20 millimetres (0.79 in) cannon in each, as well as a dorsal turret with two 0.5 in (12.7 mm) M2 Browning machine guns. The cockpit area was the same as the Mariner's. It first flew in 30 May 1948.

The first of 167 production P5M-1 aircraft was produced in 1951, flying on 22 June 1951. Changes from the prototype included a raised flight deck for improved visibility, the replacement of the nose turret with a large radome for the AN/APS-44 search radar, the deletion of the dorsal turret, and new, streamlined wing floats. The engine nacelles were lengthened to provide room for weapons bays in the rear.

The P5M-1 was followed by 116 P5M-2 planes. These had a T-tail to put the tail surfaces out of the spray, an AN/ASQ-8 MAD boom at the rear of the tail-tip, no tail guns (the gun position replaced by the antenna for the AN/APN-122 Doppler Navigation Set), better crew accommodation and an improved bow to reduce spray during takeoff and landing.

The last flying boat operations of the United States Navy were Market Time patrols of VP-40.  Maritime surveillance began in February 1965 to locate small craft transporting supplies from North Vietnam to Viet Cong units in South Vietnam.  VP-40 operated from seaplane tenders and patrolled off the Mekong delta between Phú Quốc and Vung Tau.  The last U.S. Navy P5M, redesignated as an SP-5B, was flown to NAS Patuxent River, Maryland on 12 July 1968 for interim storage pending construction of display area at the Smithsonian Institution in Washington, DC. As a display area at Smithsonian did not materialize, the aircraft was later relocated to the National Museum of Naval Aviation at NAS Pensacola, Florida where it is currently on display.

Seven P5M-1Gs and four P5M-2Gs were built for the United States Coast Guard for air-sea rescue service, but the service found the planes difficult to maintain and surplus to requirements. They were subsequently transferred to the U.S. Navy, which redesignated them as TP-5As and used them as training aircraft, since they had no provision for armament.

The SP-5B located at the National Museum of Naval Aviation at Naval Air Station Pensacola, Florida is believed to be the last remaining example of the Marlin. It is now displayed inside the new hangar (as of the spring of 2010) and much of the exterior has been restored. The restoration is being financed by the museum and the Mariner/Marlin Association.

Source: Wikipedia