The Martin P6M SeaMaster, built by the Glenn L. Martin Company, was a 1950s strategic bomber flying boat for the United States Navy that almost entered service; production aircraft were built and Navy crews were undergoing operational conversion, with a service entry about six months off, when the program was cancelled on 21 August 1959. Envisioned as a way to give the Navy a strategic nuclear force, the SeaMaster was eclipsed by the Polaris submarine-launched ballistic missile. Due to the political situation at the Pentagon, the Navy promoted the P6M primarily as a high speed minelayer.
Design and development
In the immediate postwar defense climate, the United States Air Force's Strategic Air Command was the lynchpin 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, the USS United States, a large "super carrier" to launch Navy strategic bombers from, having been a victim of budget cuts, the Navy chose instead 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 even special submarines, could be located closer to the enemy, and as mobile targets would be harder to neutralize.
The requirement, issued in April 1951, was for a seaplane able to carry 30,000 lb (13,600 kg) of "warload" with a range of 1,500 miles (2,400 km) from its aquatic base. The aircraft had to be capable of a low altitude dash at Mach 0.9 (1,100 km/h), which required an extremely capable aircraft. Both Convair and Martin submitted proposals, and the Martin one 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 planes.
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 (downward slope to the tip) 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.