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The U.S. Navy’s Last Flying Boat

By William B. Allmon
10/18/2018 • Aviation History Magazine

Development of Martin’s P6M was delayed until its time ran out.

Middle River, Maryland, July 14, 1955: Martin Aircraft’s XP6M-1 Seamaster, the world’s first jet-powered seaplane, taxied into the river for the first flight of what one pilot called “the most advanced seaplane design of its time.” What entered history books as the last seaplane flown by the U.S. Navy was built in response to a perceived threat in the early years of the Cold War, but  it was never used in its intended role.

The two atomic bombs that ended World War II in August 1945 clearly heralded a new military era. In a bid for its own nuclear weapons delivery capability, in 1947 the U.S. Navy laid the keel of United States, its first carrier capable of launching nuclear-armed aircraft. But when President Harry S. Truman signed the National Security Act on September 18, 1947, creating the U.S. Air Force, the Navy’s role in delivering nuclear weapons quickly became an issue. The Air Force was given the strategic bombing mission, Congress funneled its meager defense budget into Convair’s B-36 Peacemaker bomber, and funding for new carriers was cut from the 1950 defense budget.

The Navy was looking for a way to act as a strategic force while keeping its mission to control the seas. In the early 1950s, it had several aircraft, including the twin-engine North American AJ-1 Savage and the Lockheed PV-2 Neptune patrol plane, that could carry a single 10,000- pound nuclear bomb but were hampered by short range. In 1946 the Navy along with the National Advisory Council of Aeronautics (NACA) had begun engineering studies for a high-speed minelaying aircraft (HSML) that could double as a nuclear bomber. Two preliminary models, the DR-53 and the more advanced DR-68, showed the feasibility of advanced seaplane strike aircraft.

Based on those studies, on April 25, 1951, the Navy released Operational Requirement NOAS-04506, outlining a new concept—a force of high-speed seaplanes capable of operating in the open ocean, laying mines near enemy harbors and carrying out deep inland nuclear strikes. On July 30, 1951, the Navy’s Bureau of Aeronautics (BuAer) delivered a request to 17 aircraft manufacturers for a “transonic aircraft” capable of a speed of 600 knots at sea level with a 30,000-pound payload, to be used “primarily for low level minelaying.” Of the companies invited to bid, only longtime rivals Convair and Martin Aircraft responded.

Convair, builder of the WWII-era Consolidated PBY Catalina flying boat, submitted its proposal on December 31, 1951, for a conservatively designed aircraft with a 35- degree sweptback wing and a V-shaped tail, powered by four Wright YO-67W turbojet engines. Martin’s HSML proposal for the Model 275 Seamaster, submitted on February 7, 1952, drew on the designs of its previous large flying boats, like the PBM Mariner, JRM Mars and P5M Marlin. In designing the Seamaster, George Triable, Martin’s head engineer, used many of his company’s past seaplane innovations and some new ones that had been advanced due to the development of jet engines. Instead of bulky engine nacelles and a high drag wing, the Model 275 would have an aerodynamic hull shape, connected to a 40- degree sweptwing mounted on top, along with a T-shaped horizontal tail (previously tested on Martin’s XB-51 bomber and TM-61 guided missile) that would give it more stability. Martin would also provide a complete electronics set for navigation, minelaying and defensive measures.

On February 30, 1952, the Navy decided to fund Martin’s Model 275. That October, Martin President George M. Bunker received a contract to build two prototypes, redesignated XP6M-1, along with six follow-on models and 30 production aircraft. Both prototypes were assembled at Martin’s Middle River factory outside Baltimore, Md. The first XP6M-1 rolled out on December 31, 1954. It was a massive but gracefully streamlined aircraft with a 102- foot wingspan, a length of 133 feet and a fuselage that was 19 feet wide. Four Allison J71-A-4 afterburning jet engines mounted on top of its sweptback drooping wings, with integral floats built into the wingtips, provided 13,000 pounds of thrust each. Near the aft end of the hull were two hydroflaps that served both as a rudder or water brake and as a dive brake during flight, with little trim change. Another ingenious feature, first used in Martin’s XB-51 bomber, was its rotary bomb bay doors, located in the Seamaster’s center of gravity. The clamshell-shaped doors, sealed by inflatable rubber gaskets to preserve the hull’s watertight integrity, could rotate 180 degrees and open with little of the aerodynamic buffeting caused by conventional bomb bay doors. The plane could carry a total of 30,000 pounds of bombs or mines, or an AN/ASQ-29 camera pod, and was equipped with two remote-controlled tail-mounted 20mm cannons.

The aircraft’s four-man crew—pilot, copilot, navigator/radio operator and weapons officer—was housed in a pressurized, armor-plated flight deck. Ejection seats were installed for the pilots, and an escape chute extended from the flight deck to the bottom of the hull for the rest of the crew.

The Seamaster’s design blended the best aerodynamic and hydrodynamic advances of its day. “The aircraft was beautiful,” Navy pilot James S. Russell recalled, “graceful in lines, highly streamlined for a flying boat, and the quintessence of seaplane design.”

After several months of structural and engine tests, on July 14, 1955, the first Seamaster prototype, with Martin’s chief test pilot George Rodney, co-pilot Maurice “Maury” Bernhard and flight engineers Herb Scudder and Henry Conlon at the controls, taxied out into the Middle River for its first flight. As Rodney lifted the huge plane out of the water, one eyewitness later recalled the Seamaster took to the air “as easily as it had to water.” Rodney described the hour-and-40-minute flight as “very uneventful,” adding, “That’s the best thing you can say for an event of this kind.”

For the next six weeks, from July to September 1955, test pilots wrung out the Seamaster’s design. “It handled more like a fighter than a bomber,” Rodney recalled, “with all the other performance characteristics of comparable land-based aircraft.” The Seamaster’s water handling qualities were also excellent. “With its high hull it required no special piloting techniques except in extremely high seas,” Rodney wrote. “It would handle sea states of 3 to 5 feet with ease, and could cope with sea states in the 6- to 9-foot range.”

The early tests did not all go smoothly. Almost every flight involved engine work, and several engines had to be replaced. Rodney recalled that the pilots found the Seamaster’s cockpit “about the busiest ever invented….Pilots had to pay attention to closing the auxiliary intakes, lowering the wing flaps…keeping the nose at trim angle, and dealing with flameouts and fire warnings.” Despite engine problems, by the end of September 1955, the XP6M-1 had completed 25 flying hours, and Navy confidence in the program remained high.

On November 2, 1955, Admiral Arleigh Burke, U.S. chief of naval operations, along with Britain’s Admiral of the Fleet Lord Louis Mountbatten, toured Martin’s Middle River plant and observed a low altitude flyby of the first XP6M-1, one of its few public showings. “Our distinguished guests were favorably impressed and made many enthusiastic and laudatory comments,” Navy pilot Russell recalled.

In December 1955, BuAer sent an experienced test pilot team, consisting of Commander H.C. Weart and Lt. Cmdrs. Victor Utgoff and Ernie Horrell, from the Naval Air Test Center at Patuxent River, Md., to evaluate the Seamaster prior to the Navy’s accepting the plane. On December 7, Horrell took the Seamaster up on a 73-minute flight. Landing at 1430 hours, Horrell returned to Middle River, while Utgoff, Martin co-pilot Bernhard and flight engineers Jim Hentschell and Herb Scudder took off on the day’s second flight at 1507 hours.

Climbing to 8,700 feet, Utgoff headed south toward the Potomac River, where oyster plant operator Charles Davis saw the Seamaster fly over. “The moment I sighted it I felt something was funny,” he remembered. “It was trailing two big plumes of smoke.” Suddenly, as Davis watched, the Seamaster exploded. “Seconds later a huge ball of fire spurted from the center of the plane…. There was a terrific explosion….The plane seemed to come apart in two major pieces….Smaller parts fell through the air.” None of the crew survived. Testing of the second XP6M was suspended.

By March 5, 1956, divers had recovered 90 percent of the wreckage, which was examined by a team of Martin engineers and experts from the Navy, Air Force and NACA. Their data, along with statements from 37 eyewitnesses, were fed into Martin’s mainframe computer. On July 8, 1956, Martin released an accident report listing a “minor explosion in the center wing stub,” broken or snapped control cables, loss of “one or two different hydraulic systems” and pilot error as possible causes of the accident.

While the investigation continued, numerous changes were made to the second XP6M-1, including ejection seats for the entire crew and more elaborate telemetry monitoring devices. Testing began on May 18, 1956, when George Rodney and veteran Martin test pilot Robert S. Turner took off, climbed to 40,000 feet and reached a speed of Mach .8 during a trouble-free hourlong flight before making a “rock solid” landing back at Middle River.

Over the next seven months the second Seamaster completed 23 flights. Its 24th came on November 9, 1956, with Martin pilots Turner and William Cunningham at the controls, and flight engineers Bill Compton and Tom Kenney manning the telemetry equipment. Turner performed two openings and closings of the bomb bay doors, then pushed over into a slight dive, reaching Mach .87 before leveling out over the Chesapeake Bay Bridge at 22,000 feet. Martin tower radioed Turner, ordering him to repeat the test at maximum speed.

Turner nosed the XP6M down, held the huge plane in a full power dive for five seconds, reaching Mach .9, then pulled back on the yoke. “I pulled back on the thing, and then there was, as far as I can remember, nothing but a sharp pitch up at that time,” Turner later wrote. He pushed the yoke forward, but the Seamaster just continued climbing.

Martin test pilot Oliver F. Brown, watching from the cockpit of a North American FJ-2, saw the XP6M-1 climbing vertically. “Redbird, Redbird,” he radioed. “You’re breaking up. Bail out!” Turner, Cunningham, Compton and Kenney ejected. The aircraft exploded at 6,000 feet near Odessa, Del. Turner and his crew parachuted to safety and were giving their statements at Middle River by 1800 hours. This time the accident report concluded that a malfunction in the vertical stabilizer forced the plane to pitch up and fall into a flat spin. Martin instituted modifications, but they resulted in considerable delays. By June 1957, the Seamaster program had cost $205.4 million, and on June 28, production was cut from 30 to 24, then to 16 aircraft.

Work on the six follow-up test aircraft continued. New longitudinal control systems were installed, along with new elevators on top of the T-shaped tail and reshaped flaps on the wings. On January 28, Ship No. 2, with Rodney and Turner at the controls, took off on a successful 2l⁄2-hour flight. There were no other crashes during the development program.

By September 1958, five YP6M-1s were being tested by Martin and the Navy. At the same time, the Navy developed an extensive support infrastructure for the Seamaster, breaking ground for the first jet seaplane base at Harvey Point, N.C., and modifying the seaplane tender Albemarle to service jet aircraft at the Philadelphia Navy Yard.

In early 1959, Martin experimented with using the Seamaster as an aerial tanker. The entire refueling package, consisting of a 95- foot-long hose and drogue, drawing fuel from the P6M’s transfer tank at 9,500 gallons per minute, could be loaded aboard the aircraft at sea. Successful dry hookups were made with Grumman F9F-8 Cougar and F11F-1 Tiger fighters, and it seemed feasible that the system could also be used with other Navy aircraft. Despite this, the Seamaster’s bombing mission quickly overshadowed the plane’s auxiliary mission.

The first production Seamaster, the P6M-2, with Allison J75-P-2 turbojet engines replacing the original J71-A-4 power plants, was delivered to the Navy on February 17, 1959. But even as Navy pilots were training, its price was soaring. On November 24, 1958, after spending an additional $205 million, the Seamaster contract was cut from 16 to eight P6M-2s, and work stopped on the YP6M-1s on March 1, 1959.

Delays in production caused the Seamaster to be overshadowed by the Polaris submarine-launched ballistic missile and advanced carrier-borne jet fighters. After a report stating its combat potential would not be significantly increased by the addition of eight P6M-2s to the fleet, the Navy notified Martin of the P6M’s cancellation on August 21, 1959.

The six YP6M-1s and three P6M-2s delivered, after flying a total of 535 hours and 56 minutes, were scrapped. The Seamaster’s cancellation, however, had little permanent effect on Martin Aircraft, which had already branched out into missile and electronic technology.

 

Originally published in the May 2007 issue of Aviation History. To subscribe, click here

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