Martin P-6M SeaMaster – The End of Martin

The Martin P-6M SeaMaster was a nuclear warplane set to be the centerpiece of the
US Navy’s aborted Seaplane Strike Force, an aerial regiment designed to act as a
deterrent to Soviet aggression on the high seas.

After a promising, and at the same timedeadly, developmental phase, the SeaMaster fell from grace due to factors beyond its control, exiling a once exciting prospect to the scrapheap of aviation history, while at the same time motivating its manufacturer to completely change industries.

The P-6M was a great looking seaplane.
The P-6M was designed as a nuclear bomber.

Conents

Background

In the post-World War II atmosphere, the ability of Cold War powers to possess nuclear
strike capabilities became increasingly important.

With the US Air Force already has formulated a Strategic Air Command (SAC) of nuclear strike bombers, the US Navy made moves to establish its own nuclear seaplane fleet.

USS Enterprise, the "Galloping ...
USS Enterprise, the "Galloping Ghost" of WWII

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They envisioned a Seaplane Striking Force (SSF) that, operating alongside ships and
even submarines could strike at any time in the same fashion as the SAC, and that
could also carry out other duties such as reconnaissance, conventional bombing, and
the laying of mines, which would be particularly effective against the Soviet Navy, whose
only pathway to the open oceans was through a series of bottlenecks that could easily
be set down with explosives.

The P-6M could reach Mach .9.
The P-6M would have operated in typical bomber capacity against the Soviet Navy.

In April 1951, the Navy announced they required a nuclear-armed seaplane with several specifications. It needed to carry a war load of 30,000 pounds that could
reach a target up to 1,500 miles away, as well as fly at Mach 0.9 at its fastest in low
altitudes. In the subsequent proposal stage, Martin and Convair battled it out, with Martin
eventually being declared winner and being awarded the contract on October 31st
1952.

They were tasked with producing two prototypes, one that could act as a static test
vehicle and another more complete model, designated by the Navy as ‘XP6M-1’ but
internally referred to by the company as ‘Model 275’.

The Navy soon requested a further 6 test versions, known as the ‘YP6M-1’ and another 24 full-production units, which were given the moniker ‘P6M-2’ by the Navy but nicknamed ‘SeaMaster’ by Martin employees.

These were enough aircraft for the Navy to perform all evaluation required.
All six of the SeaMasters.

Leading the design team was George Trimble, chief of Martin’s advanced design
department, who was to liaise closely with the hydrodynamicist J.D. Pierson and the
aerodynamicist J.L. Decker.

The Martin team modified the hull of its existing XP5M-1 flying boat prototype as a basis for the SeaMaster, amending it with a length to beam ratio of 15:1 so that it could more easily travel through air and water, and changing its name to the ‘Martin Model 270’.

Testing

The first SeaMaster prototype was completed on December 21st 1954 and took to the
skies for the first time on July 14th 1955, where it was operated by Martin test pilot
George Rodney, whose flight revealed a design flaw with the engine, which had a
tendency to scorch the rear fuselage.

After the public announcement of the second SeaMaster prototype in November 1955 by the Navy, disaster would strike a month later on December 21st.

The P-6M caused quite the splash on take off!
The XP-6M-1 SeaMaster on take off roll. Look at the spray!

Founder Glenn L. Martin having died two days before, the company was once again hit
with tragedy when the first SeaMaster XP6M-1 prototype, one of the last craft to be
painted in blue before the Navy switched their color scheme to a grey and white
combination, crashed into Cheapasake Bay on a routine test run, with all 4 crew
perishing, including one of the most experienced US Navy seaplane pilots of his
generation, lieutenant commander Victor Utgoff, who was just 40 years old.

Analysis after revealed there had been a problem with the control system, which had
caused the nose to pitch sharply downwards, tearing the engines away from the wings,
which under the resulting air-load started to bend down to such an extent that they
touched the hull underneath and snapped off.

As a result, the second SeaMaster prototype was fitted with extra safety equipment, including new flight instrumentation and ejection seats, with testing recommencing in May 1956.

The YP-6M was for testing purposes.
The engines were mounted above wing to stop them ingesting water.

However, the second model was also to prove extremely unsafe, with the crew of 4
forced to escape through a hatch located on the aft side of the wing, in the first recorded
American multiple ejection, after it careened out of control on November 9th 1956,
performing an incredibly tight loop before falling apart.

This time, the problem was traced back to a miscalculation in the modified tail configuration that was being evaluated at the time.

Despite the destruction of the two prototypes, the Navy continued to pursue the
program with conviction, allocating funding for the creation of a beaching cradle which
would allow the SeaMaster to taxi in and out of water, customizing existing ships with
SeaMaster landing bays, and fitting Navy submarines with SeaMaster support vessels.

The SeaMaster was indeed impressive in these early stages, at the time breaking the
world altitude and speed records.

The Navy thought the P-6M-2 would be a much better aircraft.
The P-6M-2 SeaMaster was an improved variant.

Unperturbed by past failures, the first pre-production YP6M-1, which was revamped to
include Allison engines spaced out to prevent exhaust blast from hitting the wing, was
presented in November 1957, with 5 more SeaMasters being manufactured in 1958 for
testing, resumed that same year and with a focus on the discharge of conventional and
nuclear munitions as well as photo-reconnaissance.

Pilots were impressed with the improved model’s handling capabilities, noting it was more characteristic of a fighter rather than a bomber. After a much smoother assessment period, the first production version of the SeaMaster was rolled out in early 1959, with 2 more being finished by the summer.

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The SeaMaster

The Martin P-6M SeaMaster possesses a pressurized cockpit manned by a crew of 4
comprising of a pilot, navigator operator, radio operator, and a flight engineer was 9.88
meters in height, 40.84 meters in length, had an empty weight of 41,400 kilograms, a
max loaded weight of 80,000 kilograms, and could operate in 1.8. to 2.75 meters deep
sea.

The hull is clearly visible from this angle.
From underneath the SeaMaster looks unusual.

Replete with an aerial refueling probe and Sperry navigation, flight control, and autopilot
systems, it was propelled by four Pratt & Whitney J75-P-2 turbojet power-plants that
gave the aircraft a maximum speed of 0.9 Mach and an altitude ceiling of 40,000 feet.

In order to avoid water spray, it also featured staggered engine exhausts mounted
above the wings, which were swept back at an angle of 40 degrees, had a wingspan of
31.37 meters, a wing area of 176 square meters, and were capped with wingtip tanks
that could also act as floats which helped its dock on the water.

The wing root was extremely thick at 2.5 centimeters, with the aluminum skin of the upper wing surface measuring up to 2.5 to 4mm in an effort to provide the required strength needed for
high-speed flight at low levels.

Many of the SeaMaster’s military innovations were based on Martin’s trademark
advanced XB-51 bomber. Like the XB-51, the SeaMaster had a T-tail configuration
alongside a rotating bomb bay that was pneumatically sealed, and which when
activated flipped over to release mines and other explosives at speeds of up to 600
mph.

Martin put a lot of learnings from the XB-51 into the Seamaster.
Similarities can be seen between the XB-51 and the P-6M.

If desired, a specialized probe-and-drogue kit could be installed in the bomb bay
to convert the SeaMaster into a tanker.

Elsewhere, it was also originally intended for the SeaMaster to feature a tail turret of dual 20mm cannons, which were to be remote controlled and work alongside a fire-control radar, but these were never added to the the final design, which instead removed them to make space for electronic countermeasures (ECM) equipment.

Downfall

Although the Navy originally described its new machine as “a major new anti-
submarine warfare system… able to go after enemy submarines in their home ports”,
budget constraints meant that its demand for SeaMasters considerably reduced from
the original number of 24, and throughout the 1950s, the figure was gradually
decreased to 8.

The final nail in the coffin occurred on August 21st, 1959 when the Navy discontinued
the program, which had cost $400 million, in its entirety.

By the end of the decade, the SeaMaster had become obsolete with the rise of a much cheaper nuclear deterrent, namely the Polaris ballistic submarine.

Martin made some great looking aircraft.
The SeaMaster was ultiamtely a failure.

Martin desperately tried to re-purpose the SeaMaster with a series of failed derivatives,
such as an eight-engine airliner version nicknamed the ‘SeaMistress’, and even a nuclear-powered version, eventually deemed impractical when it was realized that a much larger aircraft would be required to handle a nuclear reactor.

Shortly after, Martin reorientated their business focus entirely away from planes, settling on missiles and defensive electronics instead. In fact the SeaMaster was Martin’s last ever plane, and marked the decline in popularity of the very concept of a military flying boat, which has
since only been pursued by the Japanese and Russians.

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The SeaMasters themselves were scrapped, with only two tails, a fuselage section, and
some wing floats surviving disassembly, all of which are now exhibited at the Glenn L.
Martin Aviation Museum in Baltimore.

Interestingly, a further 4 wingtip floats were also saved by a Martins employee, who refitted them onto a catamaran.

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Specifications

  • Crew: 4
  • Length: 134 ft 4 in (40.94 m)
  • Wingspan: 102 ft 7 in (31.27 m)
  • Height: 33 ft 10 in (10.31 m)
  • Empty weight: 97,439 lb (44,198 kg)
  • Max takeoff weight: 190,000 lb (86,183 kg) in calm water
  • Powerplant: 4 × Pratt & Whitney J75-P-2 turbojet engines, 17,500 lbf (78 kN) thrust each
  • Maximum speed: 686 mph (1,104 km/h, 596 kn) at 20,000 ft (6,096 m)
  • Range: 2,083 mi (3,352 km, 1,810 nmi)
  • Service ceiling: 50,000 ft (15,000 m)
  • Rate of climb: 7,380 ft/min (37.5 m/s)