The P6M Seamaster was a top- performing aircraft for its time—and the last flying boat developed for the U.S. Navy. Designed by the Martin Company, the P6M was intended primarily for long- range minelaying and reconnaissance missions, with a secondary nuclear strike capability. In the minelaying role, the Seamaster was to mine the approaches to Soviet submarine bases, denying access to the sea and preventing submarines already at sea from returning for replenishment.
The P6M program began in July 1951 when the Navy requested 12 aircraft manufacturers to submit proposals for a high-speed, minelaying flying boat. Martin, which had built the highly successful PBM Mariner and P5M Marlin flying boats, won the design competition and the Navy proceeded with a development program of two XP6M-1 test aircraft and six YP6M-1 flight demonstration aircraft.
A graceful-looking aircraft, the Seamaster’s flying-boat hull had an extremely high length- to-beam ratio with the wings swept back 40°. It had a high T-tail and fixed wing-tip stabilizing floats. The four turbojet engines were mounted in pairs atop the shoulder-high wing. These were Pratt & Whitney J75-P-2s with 15,800 pounds thrust each in the definitive P6M-2.
The aircraft’s five-man crew consisted of pilot, copilot, navigator-minelayer, radio operator, and gunner. For defensive armament, the Seamaster had two 20- mm. cannon housed in a remote-control tail turret beneath a fire-control radome.
It was a large aircraft. The P6M-2 production version was expected to weigh about 85,000 pounds empty and almost 190,000 pounds loaded for rough- water takeoffs. (The aircraft was designed for operation in six- to eight-foot waves.) A payload of up to 30,000 pounds of mines, bombs—or cameras and flash bombs—was to be carried on a rotary bomb-bay door that formed part of the hull bottom. During bombing tests the aircraft successfully released stores at a speed of 500 miles per hour.
The Seamaster was to remain in the water for as long as six to eight months, being maintained, refueled, and rearmed by seaplane tenders and by submarines. Weapons were loaded through the top of the fuselage, enabling the aircraft to be rearmed while in the water. Similarly, engines could be replaced while the plane was afloat. Clandestine refueling of the aircraft in forward areas from submarines was proposed. Fleet submarine Guavina (SS-362) was converted to a tanker (SSO-362, later AOSS-362) to evaluate that function. She conducted at-sea refueling trials with seaplanes to develop techniques for supporting the Seamaster. (The seaplane tender Albemarle [AV-5] was modified specifically to support P6Ms.)
The first XP6M-1 flew on 14 July 1955 That aircraft crashed into the Potomac River on 7 December 1955, because of a structural failure; the second XP6M-1 crashed near New Castle, Delaware, on 9 November 1956, because of control problems. Modifications were made to the six YP6M-1 aircraft and there were no further accidents in the flight-test program.
The Navy had placed an order for 24 production P6M-2 aircraft on 29 August 1956 Engineering problems increased the costs of the aircraft and caused program delays. Although the technical problems were solved, the costs of funding the competing—and higher priority—Polaris submarine missile program led to cuts. The initial 24-plane contract was reduced to 18 aircraft on 21 June 1957, and then, on 24 November 1958, to only 8 P6M-2 aircraft.
Concurrently, the Navy announced that a Seamaster patrol squadron (VP) would be formed to explore the capabilities of the aircraft. Only four P6M-2 production aircraft were completed, however, before the entire program was canceled on 24 August 1959—one of several Navy projects halted to help pay for the acceleration of the Polaris program. By the time of the cancellation, four of the YP6M-ls had been partially disassembled and a fifth had been destroyed in static tests; all surviving aircraft were scrapped. The 12 P6M aircraft that had been completed had logged a total of 536 hours of flight time when the project was halted.
This marked the end of flying boat development by the U.S. Navy. (The development of military flying boats continued in Japan and the Soviet Union.) The P5M Marlin flying boats remained in U.S. Navy service until November 1967. The success of the land-based P-3 Orion aircraft and the high cost of supporting seaplanes (including their specialized tenders) coupled with the lack of a follow-on flying boat meant the end of an important—and colorful—era in U.S. naval aviation.