P6M SeaMaster
Encyclopedia
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 had been built and Navy crews were undergoing operational conversion, with a service entry about six months off, when the program was cancelled on August 21, 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.
'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 tender
s or even special submarine
s, 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 bombs to a target 1,500 miles (2,400 km) away from its aquatic base. The aircraft had to be capable of a low altitude attack run 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.
, but early tests showed that the engines were mounted too close to the fuselage and scorched it when afterburners were used, leading to pointing the engines slightly outward in subsequent aircraft. Flight testing was initially successful, but, on 7 December 1955, a control system fault destroyed the first prototype with the loss of all aboard. The first prototype, BuNo 138821, c/n XP-1, disintegrated in flight at 5,000 feet due to the horizontal tail going to full up in control malfunction, subjecting the airframe to 9 g stress as it began an outside loop, crashing into the Potomac River
near the junction of St. Mary's River
, killing four crew members: Navy pilot Lieutenant Commander Utgoff, and Martin employees, Morris Bernhard, assistant pilot, Herbert Scudder, flight engineer, and H.B. Coulon, flight test engineer.
Eleven months later, on 9 November 1956, the second prototype, BuNo 138822, c/n XP-2, first flown May 18, 1956, was also destroyed, due to a change made in the horizontal stabilizer control system without adequate evaluation before test flying the design. The crash occurred at 3:36 p.m. near Odessa, Delaware
due to a faulty elevator jack. As the seaplane nosed up at ~21,000 feet and failed to respond to control inputs, the crew of four ejected, pilot Robert S. Turner, co-pilot William Cunningham, and two crew all parachuting to safety. The airframe broke up after falling to 6,000 feet before impact.
The first pre-production YP6M-1 was completed about a year later, with testing resuming in January 1958
.
Five more were built in 1958 when the Navy announced that Harvey Point Defense Testing Facility
in Hertford, North Carolina, would serve as the testing grounds for the fleet of Martin P6M SeaMasters. These aircraft were fitted with test versions of the full combat equipment suite and were used for bombing, mine laying and reconnaissance evaluations. The P6M-1 test program was mostly successful, however the J71 engines proved far less reliable than required. The P6M-1 had spray ingestion problems at high gross weight which precluded takeoffs except under ideal conditions. The P6M-1 also had a serious control deficiency due to porpoising under some trim settings. These deficiencies resulted in the P6M-1 program being cut, as it was no longer considered possible for it to be a successful asset. The P6M-1 had been generally successful, the airplane was designed to meet a demanding set of specifications, and had mostly achieved them.
The Navy and Martin felt that a new version, the P6M-2 would provide a useful aircraft. The first was rolled out in early 1959. Changes included new, more powerful Pratt & Whitney J75 engines, an aerial refueling
probe, improved avionics, and a canopy with better visibility. A buddy refueling drogue kit had also been developed to fit in the bomb bay. Three had been built by summer 1959 and Navy crews were moving them through operational conversion when the program was abruptly canceled in August of that year.
The P6M-2 was an impressive aircraft; its Mach 0.9 (1,100 km/h) performance "on the deck" could be equaled by few aircraft of the time, and few today. The planes were built incredibly tough, with the aircraft skin at the wing roots over one inch (25 mm) thick. The men managing the test program were shocked when the docile and pleasant handling characteristics of the P6M-1 were replaced by some severe compressibility effects above Mach 0.8. These included rapid changes in directional trim, severe buffeting, and wing drop requiring high control inputs to counter. Until those problems were fixed, the P6M-2 could not be considered for use by the Fleet. The problems were caused by the larger engine nacelles required for the J75s. There were also problems on the water, including a tendency for the tip floats to dig in under certain situations, and engine surges. These problems were eventually solved, but time had run out for the SeaMaster just as the first crews were training for its operational debut. The major defense budget cuts of the Eisenhower administration were forcing the Navy to make choices. In August 1959 Martin was told to halt operations; the program was going to be canceled. Seaplanes were a small community in Naval Aviation, and the P6M, significantly over budget and behind schedule, was competing with aircraft carriers for funding. The Navy had an impending superior system for the nuclear strike role, the Fleet Ballistic Missile Submarine.
Although the technology of the P6M was phenomenal, in the age of the ICBM and SLBM, the manned bomber was considered an expensive, unreliable way to deliver nuclear weapons. The P6M program had already cost $400 million (about $2.5 billion ) and could not be justified without the strategic mission.
All of the aircraft were scrapped. Some tail sections were retained for testing, and one of these is now in the Glenn L. Martin museum.
Martin tried unsuccessfully to market the technology in the civilian market, but there were no takers, and the company soon abandoned the aircraft business entirely to focus on missiles and electronics. The P6M was the final aircraft constructed by the Glenn L. Martin Company.
Glenn L. Martin Company
The Glenn L. Martin Company was an American aircraft and aerospace manufacturing company that was founded by the aviation pioneer Glenn L. Martin. The Martin Company produced many important aircraft for the defense of the United States and its allies, especially during World War II and the Cold War...
, was a 1950s strategic bomber
Strategic bomber
A strategic bomber is a heavy bomber aircraft designed to drop large amounts of ordnance onto a distant target for the purposes of debilitating an enemy's capacity to wage war. Unlike tactical bombers, which are used in the battle zone to attack troops and military equipment, strategic bombers are...
flying boat
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
for the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
that almost entered service; production aircraft had been built and Navy crews were undergoing operational conversion, with a service entry about six months off, when the program was cancelled on August 21, 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 ForceUnited States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
's Strategic Air Command
Strategic Air Command
The Strategic Air Command was both a Major Command of the United States Air Force and a "specified command" of the United States Department of Defense. SAC was the operational establishment in charge of America's land-based strategic bomber aircraft and land-based intercontinental ballistic...
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
USS United States (CVA-58)
USS United States , the third ship of the United States Navy named for the nation, but canceled during construction, was to be the lead ship of a new design of aircraft carrier. On 29 July 1948 President Harry Truman approved construction of five "supercarriers", for which funds had been provided...
, 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 tender
Seaplane tender
A seaplane tender is a ship that provides facilities for operating seaplanes. These ships were the first aircraft carriers and appeared just before the First World War.-History:...
s or even special submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, could be located closer to the enemy, and as mobile targets would be harder to neutralize.
The requirement, issued in April 1951
1951 in aviation
This is a list of aviation-related events from 1951:-Events:* Three aerial refueling points are installed on a modified United States Air Force B-29 Superfortress, making it the worlds first triple-point aerial tanker...
, was for a seaplane able to carry 30,000 lb (13,600 kg) of bombs to a target 1,500 miles (2,400 km) away from its aquatic base. The aircraft had to be capable of a low altitude attack run at Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
0.9 (1,100 km/h), which required an extremely capable aircraft. Both Convair
Convair
Convair was an American aircraft manufacturing company which later expanded into rockets and spacecraft. The company was formed in 1943 by the merger of Vultee Aircraft and Consolidated Aircraft, and went on to produce a number of pioneering aircraft, such as the Convair B-36 bomber, and the F-102...
and Martin
Martin
Martin may refer to:-In Europe:Croatia* Martin, Croatia, a village in SlavoniaSlovakia*Martin, SlovakiaSpain*Martín, a tributary of the Ebro river*Martín del Río, a town in Aragón, SpainSwitzerland*Martin , a town in Val Poschiavo...
submitted proposals, and the Martin
Martin
Martin may refer to:-In Europe:Croatia* Martin, Croatia, a village in SlavoniaSlovakia*Martin, SlovakiaSpain*Martín, a tributary of the Ebro river*Martín del Río, a town in Aragón, SpainSwitzerland*Martin , a town in Val Poschiavo...
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
Ramjet
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
engine, but this ran into problems and a more conventional Allison J71-A-4
Allison J71
|-External links:*...
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
Anhedral
* Anhedral angle, the downward angle from horizontal of the wings or tailplane of a fixed-wing aircraft* Anhedral , a rock texture without crystal faces or cross-section shape in thin section...
(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
Martin XB-51
|-See also:-References:NotesBibliography* Andrade, John M. U.S. Military Aircraft Designations and Serials since 1909. Earl Shilton, Leicester, UK: Midland Counties Publications, 1979. ISBN 0-904597-22-9....
bomber prototype were used, including an all-flying "T" tail
Stabilator
A stabilator is an aircraft control surface that combines the functions of an elevator and a horizontal stabilizer...
and a rotating bomb bay
Bomb bay
The bomb bay or weapons bay on some military aircraft is a compartment to carry bombs, usually in the aircraft's fuselage, with "bomb bay doors" which open at the bottom. The bomb bay doors are opened and the bombs are dropped when over the target or at a specified launching point.Large-sized...
—pneumatically sealed against seawater in the P6M.
Operational history
First flight of the XP6M-1 came on 14 July 19551955 in aviation
This is a list of aviation-related events from 1955:- Events :* The United Kingdoms first atomic bomber unit, the Royal Air Forces No. 138 Squadron, becomes operational, flying Vickers Valiants.-January:...
, but early tests showed that the engines were mounted too close to the fuselage and scorched it when afterburners were used, leading to pointing the engines slightly outward in subsequent aircraft. Flight testing was initially successful, but, on 7 December 1955, a control system fault destroyed the first prototype with the loss of all aboard. The first prototype, BuNo 138821, c/n XP-1, disintegrated in flight at 5,000 feet due to the horizontal tail going to full up in control malfunction, subjecting the airframe to 9 g stress as it began an outside loop, crashing into the Potomac River
Potomac River
The Potomac River flows into the Chesapeake Bay, located along the mid-Atlantic coast of the United States. The river is approximately long, with a drainage area of about 14,700 square miles...
near the junction of St. Mary's River
St. Marys River (Maryland)
The St. Marys River is a river in southern Maryland in the United States. It rises in southern St. Mary's County, and flows to the southeast through Great Mills, widening into a tidal estuary near St. Marys City, approximately wide at its mouth on the Potomac River, near the Chesapeake...
, killing four crew members: Navy pilot Lieutenant Commander Utgoff, and Martin employees, Morris Bernhard, assistant pilot, Herbert Scudder, flight engineer, and H.B. Coulon, flight test engineer.
Eleven months later, on 9 November 1956, the second prototype, BuNo 138822, c/n XP-2, first flown May 18, 1956, was also destroyed, due to a change made in the horizontal stabilizer control system without adequate evaluation before test flying the design. The crash occurred at 3:36 p.m. near Odessa, Delaware
Odessa, Delaware
Odessa is a town in New Castle County, Delaware, United States. The population was 364 at the 2010 census. Originally founded as Cantwell's Bridge in the 18th century, the name was changed in the 19th century, after the Ukrainian port city of the same name...
due to a faulty elevator jack. As the seaplane nosed up at ~21,000 feet and failed to respond to control inputs, the crew of four ejected, pilot Robert S. Turner, co-pilot William Cunningham, and two crew all parachuting to safety. The airframe broke up after falling to 6,000 feet before impact.
The first pre-production YP6M-1 was completed about a year later, with testing resuming in January 1958
1958 in aviation
This is a list of aviation-related events from 1958:- Events :* Gulfstream Aerospace is founded in Savannah, Georgia, in the United States.* The Argentine Navy acquires its first aircraft carrier by purchasing HMS Warrior from the United Kingdom....
.
Five more were built in 1958 when the Navy announced that Harvey Point Defense Testing Facility
Harvey Point
The Harvey Point Defense Testing Activity facility, owned by the Department of Defense, is located on a peninsula in Perquimans County, North Carolina, along the Albemarle Sound, near the city of Hertford, NC. Established in World War II as an operating base for sea planes conducting anti-submarine...
in Hertford, North Carolina, would serve as the testing grounds for the fleet of Martin P6M SeaMasters. These aircraft were fitted with test versions of the full combat equipment suite and were used for bombing, mine laying and reconnaissance evaluations. The P6M-1 test program was mostly successful, however the J71 engines proved far less reliable than required. The P6M-1 had spray ingestion problems at high gross weight which precluded takeoffs except under ideal conditions. The P6M-1 also had a serious control deficiency due to porpoising under some trim settings. These deficiencies resulted in the P6M-1 program being cut, as it was no longer considered possible for it to be a successful asset. The P6M-1 had been generally successful, the airplane was designed to meet a demanding set of specifications, and had mostly achieved them.
The Navy and Martin felt that a new version, the P6M-2 would provide a useful aircraft. The first was rolled out in early 1959. Changes included new, more powerful Pratt & Whitney J75 engines, an aerial refueling
Aerial refueling
Aerial refueling, also called air refueling, in-flight refueling , air-to-air refueling or tanking, is the process of transferring fuel from one aircraft to another during flight....
probe, improved avionics, and a canopy with better visibility. A buddy refueling drogue kit had also been developed to fit in the bomb bay. Three had been built by summer 1959 and Navy crews were moving them through operational conversion when the program was abruptly canceled in August of that year.
The P6M-2 was an impressive aircraft; its Mach 0.9 (1,100 km/h) performance "on the deck" could be equaled by few aircraft of the time, and few today. The planes were built incredibly tough, with the aircraft skin at the wing roots over one inch (25 mm) thick. The men managing the test program were shocked when the docile and pleasant handling characteristics of the P6M-1 were replaced by some severe compressibility effects above Mach 0.8. These included rapid changes in directional trim, severe buffeting, and wing drop requiring high control inputs to counter. Until those problems were fixed, the P6M-2 could not be considered for use by the Fleet. The problems were caused by the larger engine nacelles required for the J75s. There were also problems on the water, including a tendency for the tip floats to dig in under certain situations, and engine surges. These problems were eventually solved, but time had run out for the SeaMaster just as the first crews were training for its operational debut. The major defense budget cuts of the Eisenhower administration were forcing the Navy to make choices. In August 1959 Martin was told to halt operations; the program was going to be canceled. Seaplanes were a small community in Naval Aviation, and the P6M, significantly over budget and behind schedule, was competing with aircraft carriers for funding. The Navy had an impending superior system for the nuclear strike role, the Fleet Ballistic Missile Submarine.
Although the technology of the P6M was phenomenal, in the age of the ICBM and SLBM, the manned bomber was considered an expensive, unreliable way to deliver nuclear weapons. The P6M program had already cost $400 million (about $2.5 billion ) and could not be justified without the strategic mission.
All of the aircraft were scrapped. Some tail sections were retained for testing, and one of these is now in the Glenn L. Martin museum.
Martin tried unsuccessfully to market the technology in the civilian market, but there were no takers, and the company soon abandoned the aircraft business entirely to focus on missiles and electronics. The P6M was the final aircraft constructed by the Glenn L. Martin Company.