The Martin P6M SeaMaster was an experimental strategic bomber flying boat built by the Glenn L. Martin Company for the United States Navy that almost entered service; production aircraft were built and Navy crews were undergoing operational training, with service entry expected in about six months, when the program was cancelled on 21 August 1959. Envisioned as a strategic nuclear weapon delivery system for the Navy, the SeaMaster was eclipsed by the Polaris submarine-launched ballistic missile (SLBM). Due to the political situation at the Pentagon, the Navy promoted the P6M primarily as a high speed minelayer. In the immediate postwar defense climate, the United States Air Force's Strategic Air Command was the linchpin of the United States' security as the sole means of delivery of the nation's nuclear arsenal. The Navy saw its strategic role being eclipsed by the Air Force and knew both its prestige and budgets were at stake. Its first attempt to address this came in the form of the USS United States, a large supercarrier intended to launch Navy strategic bombers. This was cancelled in 1950 shortly after her keel was laid down, a victim of budget cuts and US Air Force interference. In response, the Navy chose to create a "Seaplane Striking Force", useful for both nuclear and conventional warfare, including reconnaissance and minelaying. Groups of these planes supported by seaplane tenders or special submarines could be located close to the enemy, and being mobile, they would be hard to neutralize. The requirement issued in April 1951 was for a seaplane able to carry a 30,000 lb (14,000 kg) warload over a range of 1,500 mi (1,300 nmi; 2,400 km) from its aquatic base. The aircraft was to be capable of a low altitude dash at Mach 0.9 (1,100 km/h). Both Convair and Martin submitted proposals, and the Martin proposal was chosen as more promising. An order for two prototypes was issued which was projected to lead to six pre-production aircraft and a projected twenty-four production aircraft. Ultimately, 12 aircraft were buiilt. Originally the plane was to have a Curtiss-Wright turbo-ramjet engine but this ran into problems and a more conventional Allison J71-A-4 turbojet was employed, fitted in pairs in overwing pods to keep the spray out of the intakes. Wings swept at 40° were used; they displayed a notable anhedral and were designed with tip tanks that doubled as floats on the water. Many features of Martin's XB-51 bomber prototype were used, including an all-flying "T" tail and a rotating bomb bay—pneumatically sealed against seawater in the P6M. Variants XP6M-1 prototypes, two built (BuNos 138821, 138822). Both crashed. YP6M-1 pre-production model, six built (BuNos 143822-143827). All six examples were scrapped when the program was cancelled. P6M-2 (Specifications below) production model, eight built (BuNos 145876-145899). 145877-145879 were completed and flown, 145876 and 145880-145883 were completed but not flown. Contracts for 145884-145899 were cancelled.
