In the 1950s, the U. S. Navy saw itself being left out of all-important strategic bombing duties while the Air Force seemingly monopolized the mission with 2,000 long-range bombers ready to attack the Soviet Union. The Navy worked hard to develop a strategic nuclear role by positioning larger aircraft aboard its aircraft carriers, but such carrier-based aircraft were never competitive with the Air Force’s Strategic Air Command. The solution for the Navy, at least as some planners saw it, was to use large seaplanes for strategic missions, freeing the crews from dependence on easily targeted airfields with fixed runways.
The term Seaplane Striking Force (SSF) came into use in the Pentagon. And the most ambitious seaplane ever planned in the United States came into being – the Martin P6M SeaMaster, a graceful, four-jet flying boat almost the size of a B-52 Stratofortress. When details of the SeaMaster’s design were disclosed – some, with Navy cooperation, appearing for the first time in Roy Crane’s syndicated Buz Sawyer comic strip – one observer called the SeaMaster “elegant.” Even today, looking back, it is difficult not to be impressed with the beauty and functionality of this large, highly original aircraft.
The Navy and the Glenn L. Martin Company envisioned a striking force of P6M SeaMaster seaplanes carrying out nuclear bombing missions and pioneering atomic energy as a source of power for aircraft. Martin built nine P6M SeaMasters. The enthusiasm over their graceful appearance was well founded, but their story turned out to embody tragic elements.
Design work on the SeaMaster began when the Navy laid down a 1953 requirement for a high performance, multirole flying boat. Known to the manufacturer as the Martin Model 275, the design that emerged had an all-metal hull of high length/beam ratio, mounting a high-set wing, sharply swept at 40 degrees, which incorporated so much anhedral (or negative dihedral) that the stabilizing floats on the wingtips were attached permanently.
The P6M-1 SeaMaster had a T-tail. Mounted above the wing to minimize spray ingestion were four 13,000-pound thrust Allison J71 turbojet engines with afterburners. The pressurized flight compartment had provision for a crew of five.
Built by Martin (a predecessor of today’s Lockheed Martin) in Baltimore and tested in the waters of the Chesapeake Bay, the first XP6M-1 made its maiden flight on July 14, 1955. It was one of the last Navy planes to be painted in the familiar blue color scheme before the service changed, that year, to a gray and white color combination.
On Dec. 7, 1955, two days after the death of aviation pioneer Glenn L. Martin, 69, who had created the great company bearing his name, the no. 1 SeaMaster broke up, exploded, and burned on a flight over the Chesapeake. Four men died, including Lt. Cmdr. Victor Utgoff, 40, one of the Navy’s most experienced seaplane pilots.
The second SeaMaster flew on May 18, 1956. The Navy placed an order for six J71-powered pre-production XP6M-1 flying boats. On the basis of early flight tests, the Navy placed a subsequent order for 24 production P6M-2 aircraft, which differed in being powered by 17,000-pound non-afterburning Pratt & Whitney J75-P-2-PW turbojet engines and fixed some of the faults found in the XP6M-1.
The SeaMaster’s ordnance delivery system was a Martin trademark, a variation of a feature found on the company’s XB-51 and B-57 bombers. This was a rotary weapons door in the hull, on a fore and aft axis, that could dispense bombs or aerial mines at speeds up to 600 mph. The ordnance could be replenished from openings on top of the hull. Pneumatic tubes sealed the opening around the hull weapons door. The weapons door rotated 180 degrees, allowing weapons to be dropped while keeping the hull sealed to prevent buffeting produced by old-fashioned bomb bay doors.
It was expected that the SeaMaster could, if necessary, be fueled from a submarine near enemy shores – an interesting precedent for the emphasis on littoral warfare adopted by the Navy in later years. The jet flying boat would then have a combat radius of up to 3,000 miles. An imaginative map drawn up in the Pentagon showed offshore SeaMasters capable of flying far enough to strike virtually every important target in the U.S.S.R – wishful thinking which ignored the risks of launching missions near an enemy’s coast.
The second SeaMaster crashed on Nov. 9, 1957. The four-man crew bailed out successfully.
Although two SeaMasters had been lost in test-flying mishaps, no serious flaws were ever found in the flying boat’s design. It was immensely strong, with the aluminum skinning at the wing roots an inch thick, and very fast, demonstrating .89 Mach at low level when the contemporary B-52 could achieve only .55 Mach.
But the Navy wasn’t really prepared to build the infrastructure it would need for a global, water-based bomber force. The Navy had no air refueling tankers, no submarines capable of refueling the SeaMaster far from home, and no handy way to cope with mechanical breakdowns in an aircraft sent afar on a solo assignment.
After three XP6M-1 and three P6M-2 aircraft had been built, contracts for remaining airframes were cancelled on Aug. 21, 1959, in a decision that was and remains controversial.
The SeaMaster weighed 160,000 pounds on takeoff, and was 134 feet long, with a wingspan of 102 feet.
Unfortunately, the SeaMaster initially “had design flaws and underperforming engines,” said Stan Piet of the Glenn L. Martin Maryland Aviation Museum in Baltimore. Both prototypes “were lost tragically in crashes that didn’t need to happen,” Piet said. Piet said that the SeaMaster “became a viable airplane by 1959, but by then they didn’t need it because they had Polaris.” While the flaws in the SeaMaster had been worked out, the Navy concluded that the concept itself was flawed, because other alternatives for the nuclear strike mission were being developed.
The Polaris submarine-launched ballistic missile (SLBM) gave the Navy a strategic nuclear mission never really achieved by carrier-based or water-borne airplanes. All of the SeaMasters were eventually scrapped, with not a single example preserved for history. The SeaMasters were the fastest flying boats ever constructed, but sadly the last aircraft that the Glenn L. Martin corporation ever built.
A highly regarded history of this remarkable aircraft, Martin P6M SeaMaster, by Piet and Al Raithel, published in 2001, is no longer in print, but co-author Piet has copies available. He can be reached at firstname.lastname@example.org.