P6M SeaMaster

The P6M Seamaster, a swept-wing seaplane powered with four jet engines and incorporating a new hull design, made its first flight on July 14, 1955. It was built by the Glenn L. Martin Company of Baltimore, Maryland. Designed for minelaying and reconnaissance tasks, and adaptable to other missions, this plane initially demonstrated great promise for the offensive potential of the operating forces. The tactical concept behind the Seamaster was that it would operate in small numbers and be refueled and rearmed by submarines or other small naval craft. It was undoubtedly the most sophisticated flying boat constructed at that time.

In speaking against building the B-36 and the notion of the heavy all-jet B-52 in the future, Rear Adm James Russell, chief of the Navy Bureau of Aeronautics, argued that the Navy's prototype jet seaplane, the P6M, could be more effective than land-based bombers. "Sea planes could also 'hide' in ocean coves and inlets around the world and be supported by ship task forces." The P6M, however, was completely incapable of carrying the size and weight of the early nuclear (atomic) weapons.

The Martin SeaMaster was designed in the early 1950s as a jet-powered seaplane bomber which could carry a nuclear weapon from virtually any body of water; lack of super-carriers at the time prevented the U.S. Navy from having a major strategic weapons strike force to compete with the Air Force and its long-range bombers. The first XP6M-1 SeaMaster flew on July 14, 1955 and the second prototype rolled out in November. This seaplane, which could operate with only a tender or submarine to provide fuel and armament, represented the zenith for U.S. seaplane development and is a good example of the aggressive innovation in aircraft design that took place in the 1950s. The SeaMaster prototype had a gross take-off weight of 160,000 lbs.

The prototype engines (Allison J71-A-4) were aligned parallel with the fuselage centerline and the intakes were along the leading edge of the wing. The wing had some anhedral (droop). These features are found on the Topping model. It was determined on initial test flights that afterburner caused excessive heat and vibration in the fuselage aft section. Both prototypes experienced in-flight breakups causing extensive redesign in the YP6M-1s. The YP units had the intakes moved back on the wing and the engines canted outwards by five-degrees; the wing was given dihedral and an all-new flight control system was installed to prevent the failures experienced by the prototypes.

In the post-World War II period, the US Air Force built up the "Strategic Air Command", a nuclear strike force of long-range bombers. The US Navy realized that the strategic nuclear mission was now of overwhelming importance, all the more so because defense budgets were being cut, and wanted to build up their own nuclear strike capability to prevent them from being overshadowed by the Air Force / SAC.

Proposals to build a "super carrier", the USS UNITED STATES, as a floating base for Navy strategic bombers were shot down in 1949, and so the Naval Bureau of Aeronautics came up with another scheme, the "Seaplane Striking Force (SSF)". The SSF envisioned a fleet of big, jet-powered seaplanes that would not only be capable of long-range nuclear strike, but would also be useful for conventional bombing, reconnaissance, and mining. Laying mines was seen as particularly important, since to reach the open seas the Soviet Navy had to pass through a number of "bottlenecks" that could be blocked by mining. The seaplanes would be able to operate from advanced areas, supported by a seaplane tender or even a submarine.

The Navy issued a request to industry in April 1951. The SSF seaplane was to carry 13,600 kilograms (30,000 pounds) of warload to a target over 2,400 kilometers (1,500 miles) from the seaplane's aquatic "base". The aircraft was to be capable of a Mach 0.9 dash at low altitude.

Convair and Martin submitted proposals, with Martin winning the competition. On 31 October 1952, the Navy awarded Martin a contract for two prototypes, with the company designation of "Model 275" and the Navy designation of "XP6M-1", plus a static test article. This initial order would presently lead to further contracts for six pre-production service evaluation machines, with the designation of "YP6M-1", and up to 24 full-production machines, with the designation of "P6M-2".

Martin gave the aircraft the name "SeaMaster". Apparently the company had run out of names starting with "Mar".

The Martin design team was led by George Trimble, an aeronautical engineer who as head of the Martin advanced design department; J.D. Pierson, a hydrodynamicist; and J.L. Decker, a aerodynamicist. Using the P5M Marlin flying boat as a starting point, they developed a revised hull design, with a length-to-beam ratio of 15:1, which was felt to offer the best efficiency in both air and water. The XP5M-1 Marlin flying boat prototype was rebuilt to test the new hull design, with this test aircraft designated the "Martin Model 270".

The original powerplant was supposed to have been a Curtis-Wright turbo-ramjet engine, but the engine development program ran into trouble, and so the decision was made to fit the SeaMaster with four Allison J71-A-4 turbojet engines with 57.87 kN (5,900 kgp / 13,000 lbf) afterburning thrust each, mounted in pairs in nacelles above the wing near the wing roots. The J71 was a derivative of the J35 axial-flow turbojet, used on the Republic F-84 Thunderjet, and originally developed by General Electric as the TG-180 but passed on to Allison for full production.

The wings featured a sweepback of 40 degrees and ended in wingtip tanks that served as floats. The wingtip floats were also fitted with gear to help dock the aircraft. The SeaMaster was to have a pressurized cockpit and crew of four, including pilot, copilot, navigator / radio operator, and flight engineer.

The SeaMaster leveraged off Martin's advanced XB-51 attack bomber design, with features such as an "all flying" tee tail and a rotating bombbay. The bombbay flipped over in flight to expose munitions or camera payloads, and was pneumatically sealed to keep it watertight. The sole defensive armament was a remote-controlled tail turret with twin 20 millimeter cannon.

The first SeaMaster prototype was rolled out in secret on 21 December 1954, and performed its first flight on 14 July 1955, with Martin test pilot George Rodney at the controls. The flight test program revealed only one serious flaw: the engines scorched the rear fuselage, and so the use of afterburner had to be limited.

The Navy publicly announced the SeaMaster in November 1955, inviting the press to witness the rollout of the second XP6M-1 prototype. Unlike the first prototype, the second prototype was fitted with operational navigation and bombing gear.

The test program continued smoothly until 7 December 1955, two days after the death of Glenn L. Martin. During a routine check flight for the first Navy pilot, the initial SeaMaster prototype crashed into Chesapeake Bay, killing all four aircrew on board.

The post-mortem revealed a control-system fault that caused the aircraft to pitch nose down, bending its wings down and ripping them off. The second SeaMaster prototype was refitted with new flight instrumentation and ejection seats. Test flights finally resumed in May 1956. Unfortunately, the second prototype went out of control on 9 November 1956 during a flight test of a modified tail configuration. The aircraft broke up, but the crew were able to eject safely. The problem was traced down to an an error in the design calculations for the tail control system.

Despite the loss of both prototypes, the Navy still remained enthusiastic about the SeaMaster. A beaching cradle was designed to allow SeaMasters to taxi in and out of the water, and two LSDs (landing ship docks), two seaplane tenders, and the submarine USS GUAVINA were sent to shipyards to fit them as SeaMaster support vessels. A home base was set up at Naval Air Station Harvey Point, near Elizabeth City, North Carolina.

The first pre-production YP6M-1 was rolled out in November 1957, with flight tests resuming in January 1958. It featured afterburning Allison J71-A-6 engines, which were visibly "toed out" to reduce the effect of exhaust blast on the rear fuselage. The engine inlets were also moved back from the leading edge of the wing, presumably to reduce water ingestion. Five more YP6M-1s were built in 1958 and participated in an extensive flight test program, performing practice drops of conventional and (dummy) nuclear munitions, and evaluating day and night photoreconnaissance pallets.

The first production P6M-2 was rolled out in early 1959. The production SeaMaster featured more powerful non-afterburning Pratt & Whitney J75-P-2 turbojet engines with 77.89 kN (7,940 kgp / 17,500 lbf) max thrust each, providing a total increase of 53.36 kN (5,440 kgp / 12,000 lbf) thrust, and permitting a substantial increase in gross weight. The engine installation was visibly different: the engine exhausts in the XP6M-1 and YP6M-2 had been staggered, but they were parallel in the P6M-2.

The increased gross weight meant the production SeaMasters sat lower in the water, and so the wing anhedral was eliminated. The P6M-2 was fitted with a new canopy with large overhead panels for improved visibility; solid-state Sperry navigation and bombing systems; and a mid-air refueling probe. A probe-and-drogue tanker kit was also developed that could be plugged into the SeaMaster's bombbay, allowing it to be quickly converted into a tanker. The SeaMaster was a futuristic aircraft, and its performance demonstrated that it wasn't just a pretty toy. The wings were built very strong for low altitude operation, with aluminum 2.5 centimeters (an inch) thick at the wing roots, and the SeaMaster was able to attain the Mach 0.9 requirement for "on the deck" flight. In contrast, the Boeing B-52 was only capable of Mach 0.55 at low altitude.

Three production P6M-2s had been completed by the summer of 1959, with all-Navy crews moving them through operational conversion for service introduction in early 1960. Five more were in construction. However, the Navy had been steadily cutting back the number of production aircraft, from 24, to 18, and then to 8, and then on 21 August 1959 cancelled the SeaMaster program completely.

There were loud protests, since the program had cost about $400 million USD and the machine was certainly whizzy, but in truth the SeaMaster was an obsolete concept. The Navy was already moving full steam ahead to a much more effective nuclear deterrent capability in the form of the Polaris ballistic missile submarine.

Martin tried to promote other seaplane designs, such as an eight-engine airliner version of the SeaMaster that was informally called the "SeaMistress", but the writing was on the wall. Martin formally abandoned the aircraft business to focus on missiles and defense electronics. The SeaMasters that had been built sat idle for over a year and were then scrapped, and sadly only bits and pieces of them survive.

The first airframe proposed by the Navy for the aircraft nuclear power program, in 1956, was based on the Martin P6M-1 Seamaster. The Seamaster seemed suited for eventual nuclear propulsion, due to its size and configuration, combined with [the] practically unlimited takeoff and landing areas water provides. The atomic Seamaster would have four modified turbojet engines, served by a single reactor. Its advantages as a platform would be low-altitude maneuverability, a large crew, high crew and aircraft utilization, and substantial payload. Seamaster would be used initially as a low-power, modest-performance seaplane for antisubmarine warfare and radar early warning, but experience with aircraft nuclear propulsion, the Navy predicted, would eventually lead to a high-speed attack plane.

During flight tests, both XP6M-1s crashed. A major redesign program followed this mishap, during which the wing was given dihedral in place of the former anhedral. other changes included the installation of more powerful engines, the jet pipes of which toed out sharply. Most important, a new, all-transistorized auto-pilot and flight control system was installed.

The Navy ordered an initial batch of 24 Seamasters, but through the delay caused by redesign work and the accompanying steep rise in costs, six aircraft were canceled. The first production aircraft, YP6M-1, flew in February 1959, and the Navy boasted how well their new aircraft could mine the Black Sea, and claimed it was "a major new anti-submarine warfare system . . . able to go after enemy submarines in their home ports." However, by this time the force of 18 aircraft had been reduced to eight, which were planned to operate as a single squadron from a new 'seadrome'. In the event, even these eight aircraft proved too expensive and only an additional three production P6M-2s Seamasters were built. The Seamaster project was terminated in the fall of 1959.

Prior to World War II several submarines had been fitted to refuel seaplanes, and during the war Germany and Japan used this technique with some success. After the war this technique was experimented with within the US Navy. It was planned to use submarines to refuel the new jet powered P6M flying boats. As part of this program AOSS-362 Guavina was converted to carry 160,000 gallons for aviation fuel. To do this blisters were added to her sides and two stern torpedo tubes were removed. When the P6M project was canceled, there was no further need for submarine tankers.

Shifted to the Philadelphia Naval Shipyard in February 1956, AV-5 Albemarle was earmarked for conversion to tend Martin P6M "Seamaster" jet flying boats. She was reassigned from the Atlantic Reserve Fleet to the Commandant, 4th Naval District, for conversion, effective 6 February 1956. Equipped with stern ramps and servicing booms to handle the "Seamaster," as well as a semi-sheltered area and a service drydock, the ship emerged from the conversion possessing the capability to serve as a highly mobile seadrome capable of supporting jet seaplanes anywhere. Albemarle was recommissioned at Philadelphia on 21 October 1957, Capt. William A. Dean in command. After fitting out, she sailed for Norfolk on 7 December, and arrived there on the 10th. The ship then sailed for Guantanamo Bay on 3 January 1958, made port there on the 7th, remaining there for ten days and carrying out shakedown training, before dropping down to Montego Bay, Jamaica. Proceeding thence back to Guantanamo, concluding her shakedown on 21 January, Albemarle steamed thence to San Juan and Trinidad, carrying out tending operations with four squadrons of Martin P5M "Marlin" flying boats and participating in "Springboard" exercises. Albemarle arrived back at Norfolk on 9 April, remaining there only five days before proceeding back to Philadelphia Naval Shipyard, where she remained under overhaul through mid-July. Returning to Norfolk on 20 July, the ship got underway for operations in the North Atlantic on 14 August, and ranged as far as the Azores before returning to Norfolk on 16 September. Over the next two months, Albemarle operated between Norfolk and Bermuda; she rounded out the year at Norfolk, arriving there on 19 November and remaining until 2 March 1959. Albemarle continued to operate out of Norfolk through 1959 and into 1960, although the cancellation of the "Seamaster" program meant that the ship would never service the aircraft for which she had been reconfigured.

NAAS Harvey Point, North Carolina was established as an NAAS on 15 June 1943 and was capable of servicing up to 48 patrol aircraft (four squadrons) at a time. It was used during WWII primarily as a training base for establishing new seaplane squadrons. During the period 7 October 1943 to late 1945, NAAS Harvey Point also served as the headquar-ters for FAW-5 and HEDRON 5-2. The NAAS portion of the base was disestablished on 1 September 1945 and the site served as a storage area for the Navy's surplus PBM Mariners. The base was reactivated in 1958 to support sea trials for the P6M Seamaster seaplanes. The demise of the Navy seaplane program resulted in the closure of the base once again in 1963.

In its last major aircraft design, Martin returned to an earlier concept of the flying boat as a bomber. By the end of the 1940's the Soviet Union had tested a nuclear bomb, and the Cold War was in full swing. The newly created Air Force was busy buying and deploying long-range bombers to deliver nuclear weapons, a monopoly viewed by the Navy as unacceptable. Noting the inherent limitations of its force of short-range carrier attack and maritime patrol aircraft, the Navy looked at several means of joining the Air Force as in strategic deterrent. A super-carrier (the United States) was designed to handle larger propeller and jet aircraft then under design. The United States ran afoul of military budget limitations and vehement opposition from the Air Force "bomber lobby." The Navy Bureau of Aeronautics then developed the concept of a "Seaplane Striking Force" centered around the development of large jet-powered seaplanes that could offer performance equal to that of land-based jets. Capable of operating from most of the earth's surface, a small number of these seaplanes could perform mining, conventional and nuclear strike, and photo reconnaissance missions that would complement those of the new Strategic Air Command. With only a tender or submarine needed for re-arming and re-fueling, the SSF promised an economical means of force projection.

Requests to industry were let in April 1951. After a short but fierce design competition with Convair, Martin was awarded contracts for two prototype XP6M-1's, six pre-production service-test YP6M-1's, and up to 24 production P6M-2's. Martin named the SSF aircraft the SeaMaster. The Navy was now in the bomber business.

Design specifications for the SeaMaster were demanding. Required to carry 30,000 pounds of payload to a target 1,500 miles away, the plane was also required to be capable of a high-speed dash at .9 Mach at low altitude. Its hull had to be stressed for open-ocean operations. Design Engineer George Trimble, hydrodynamicist J.D. Pierson, and aerodynamicist J.L. Decker led the design team. Refining work already done on the Marlin's hull design, they adopted a new length-to-beam ratio of 15 to 1 as most efficient in both air and water. The XP5M-1 airframe was rebuilt to test the new hull, redesignated Martin Model 270. Hydroflaps like those on the Marlin were fitted for dual use as air brakes.

A compound turbo/ramjet from Curtiss-Wright was initially designated as the SeaMaster powerplant. After several failures in testing, this engine was dropped in favor of modified Allison J71's, mounted in tandem overwing nacelles. The P6M had the same variable-incidence "flying" T-tail and spoiler ailerons as the XB-51, and its payload was carried in a rotating bomb-bay, pneumatically sealed to be watertight. Swept wings with slight anhedral drooped close enough to the water for wingtip tanks to serve as stabilizing floats, without the drag of struts. The overall result was an airplane with proportions so sleek and simple that they could be described as classic.

The first prototype was rolled out in secrecy on December 21, 1954, and after several months of load-verification tests the XP6M-1 finally took to the air on July 14, 1955, flown by Martin chief test pilot George Rodney. Initial tests revealed only one major problem that required a "fix": the design of the nacelles allowed the afterburner exhaust to scorch and sonically fatigue the rear fuselage. After keeping the plane's development secret, the Navy invited the press for the roll-out in November of the second prototype, which was outfitted with a complete set of navigation and bombing equipment.

All went well with the testing program until December 7, 1955 (two days after the death of Glenn L. Martin), when the first XP6M-1 prototype crashed into the Chesapeake Bay during a routine check ride for the first Navy pilot. All four members of the crew were lost. With no onboard data recorders to help, the accident-investigation team was unable to find a specific fault. Months were lost re-configuring the second prototype with test instrumentation and ejection seats for all the crew. It was not until May, 1956, that flight testing resumed with Ship #2.

By autumn, solutions were being sought for a frequent airframe buzz that plagued both prototypes. One "fix" involved locking the elevators together with the variable-incidence "flying tail." A test flight on November 9 verified that improvement in the vibration, however, in recovering from a shallow dive at high speed, pilot Bob Turner lost pitch control of the aircraft, which started a violent outside loop. The crew ejected safely as the airframe broke up. Information from the flight data recorders indicated that the modified tail configuration had been overpowered by dynamic forces at high speed, due to a previously undiscovered mathematical error in calculating loads for the hydraulic control actuators.

Even at this low point in the program the Navy BuAer still saw promise in the concept and optimistically continued funding for the SeaMaster and a number of expensive "options." A beaching cradle was designed that allowed SeaMasters to taxi in and out of the water on their own power. Two old amphibious-warfare dock ships and two conventional seaplane tenders began shipyard conversions as support ships for the SSF. The submarine U.S.S. Guavina, redesignated as an AO(SS) "oiler," was equipped to refuel SeaMasters at secret seadromes. There were also plans to use an old escort carrier equipped with a retractable rear ramp for "beaching" P6M's, which were too heavy to be hoisted aboard by cranes. Finally, an auxiliary naval air station was refurbished to serve as the SeaMasters' home base; it occupied 1,265 acres at NAS Harvey Point, near Elizabeth City, N.C.

Meanwhile service-test YP's were completed with "fixes" for the problems encountered in the prototypes. Engine nacelles were canted out five degrees from the fuselage and the intakes moved back from the wings' leading edges. Hydraulic control systems were upgraded in the tails. A year after the second crash, the first YP6M-1 was rolled out and flight testing resumed in January 1958. Five other YP's joined the program during 1958, and tests were carried out at a feverish pace. Mine-laying and navigation systems were qualified even though standard Navy mines could not yet withstand sea impact when dropped at high speed. Conventional and "special-weapon" (nuclear) practice shapes were successfully dropped from the rotary bomb-bay, and night and day photo reconnaissance pods were tested.

Early in 1959 production P6M-2's began to emerge from the Martin plant, and the full potential of the design was realized. Installation of newly developed Pratt and Whitney J75 engines gave the P6M-2's nearly 12,000 more pounds of static thrust. This allowed the gross weight to be increased to 195,000 pounds from 171,000 pounds in the YP's. Increased weight meant a greater draft for the hull, which in turn necessitated raising the wing anhedral to zero degrees. Other improvements included full-visibility canopies and transistorized Sperry navigation and bombing systems. Production P6M-2's were equipped with midair refueling probes, and "buddy-pack" refueling kits were designed to fit inside SeaMaster bomb-bays, allowing fast conversion into tankers.

Pilots reported that the planes handled well and were capable of flying Mach .89 "on the deck." This was important, as the development of radar-guided surface-to-air missiles had made low-level flying an essential part of strategic penetration missions. The SeaMaster's wings were especially strong for the extra stress of high speeds through thick air; the aluminum skin at the wing roots was an inch thick. By contrast, the Air Force's B-47 could only manage about Mach .58 at low altitude, the newer B-52 only .55.

By the summer of 1959 all-Navy crews had begun flying three P6M-2's completed so far, and it appeared that operations could begin by early 1960. Rising costs, however, had led to two cutbacks, reducing the number of production items to eighteen, then eight. Then the bottom dropped out altogether. Citing "unforeseen technical difficulties," the Navy cancelled the entire program on August 21.

The decision was and still is highly controversial. More than $400 million had been spent on equipping the SSF, but during its long gestation period newer technologies had emerged. The development of the Polaris ballistic missile and submarine had finally given the Navy its strategic deterrent. Further, the atomic powered carrier Enterprise was going into service with long range nuclear capable strike aircraft, namely, the A3D Skywarriors and supersonic A3J Vigilantes.

Stunned, Martin engineers and executives tried to generate interest in an eight-jet transport version of the P6M, whimsically dubbed the SeaMistress, a huge nuclear-powered flying boat, and a supersonic seaplane somewhat resembling the Air Force Canberra. But there were no takers. Martin Chairman George Bunker announced that the company was now in the missile and electronics business. Fifty years of aircraft design and production was at an end.

Of the SeaMaster program little remains. The aircraft languished on the D Building ramp at Middle River for over a year after the cancellation before being scrapped. The "flying tails" and two rear fuselage sections were sent to Navy test facilities, while two sets of wing floats were used by a Martin supervisor to build a catamaran. Two tails, one fuselage section, and wing floats now belong to the Glenn L. Martin Aviation Museum. The evolution of the propeller-driven flying boat in America is traced in chapter 8. Although the U.S. Navy continued to operate a few flying boats as late as the mid-1960's, the era during which this picturesque class of aircraft played an important role in civil and military aviation really ended with the close of World War II As a last effort to prolong the usefulness of the military flying boat, the Navy sponsored development of a large, jet-powered boat for long-range, mine-laying, and reconnaissance duties. Operation from bodies of water in dispersed and remote locations, with minimum support facilities, was envisioned as a means of avoiding the inherent vulnerability of large numbers of aircraft situated at congested air bases. With first flight on July 14, 1955, the Martin P6M Seamaster was developed to fill the prescribed role. Configuration of the aircraft featured a sweptback wing mounted near the top of a single-step, high-length-beam-ratio hull. Two afterburning jet engines were located side by side in each of' two nacelles mounted oil top of the wing immediately adjacent to either side of' the fuselage. (The afterburners, an unusual feature for a large subsonic aircraft, were for use oil takeoff.) Inlets swept back at nearly the same angle as the wing leading edge were found to be unsatisfactory and unswept inlets were finally adopted; exhaust nozzles were behind the trailing edge of the wing. The location of' the engines was, of course, strongly influenced by the necessity of minimizing spray ingestion during operation on the water. The horizontal tail was positioned atop the vertical fin in a T arrangement and featured a pronounced positive dihedral angle. Impingement of both jet exhaust and spray was minimized by the tail configuration. Coupled with the large vertical tail, the positive dihedral of the horizontal surface working with the negative wing dihedral gave the proper dihedral effect for the integrated configuration. The negative wing dihedral allowed the lateral balancing floats to be mounted flush against the wingtips with neither drag-producing mounting struts or pylons. The 40° sweptback wing had an aspect ratio of 5.53 and airfoil thickness ratios that varied from 11 percent at the root to 8 percent at the tip. Lift augmentation was achieved with trailing-edge flaps and with slats located over the outer portion of the leading edge; the slats can be seen in the deployed position in figure 12.16. Wing spoilers were used for roll control; elevators together with an adjustable stabilizer were used for pitch control; and a single rudder was provided for control about the yaw axis. Maneuvering on the water was enhanced by hydroflaps located on both sides of the hull afterbody. When opened individually, these flaps served as rudders for directional control while symmetrical deployment provided braking. The hydroflaps may be seen outlined in black in Figure 12.17. The Seamaster crew consisted of a pilot, copilot, navigator-minelayer, and radio armament-defense operator. All crew quarters were pressurized and each crew member was equipped with an ejection seat. [385] Armament consisted of two remotely operated 20-mm cannons located in the tail. The mine bay had a watertight rotary door, the outside of which served as part of the bottom of the hull. A rack for mounting mines or other types of stores was fastened to the inside of the door. Rotation of the door in flight provided the means for weapons delivery. With a gross weight of 167 011 pounds, the YP6M- 1was a large aircraft capable of attaining a maximum speed of 646 miles per hour (Mach 0.86) at 5000 feet and cruised at a speed of 540 miles per hour. Even higher performance was shown by the P6M-2, which had engines of higher thrust than those on the YP6M-1. From the data given in reference 200, the mission radius of the aircraft as a minelayer seems to have been about 800 miles with a payload of 30 000 pounds and 1350 miles for the high-altitude reconnaissance role. Ferry range is estimated to have been about 3500 miles. In spite of the promising characteristics of the P6M, the Navy terminated the program in August 1959 after 12 aircraft had been constructed, including 2 prototypes that had been lost. Shortage of funds coupled with demands of higher priority programs no doubt played a major part in the cancellation. The Seamaster was the last large flying boat developed in the United States, and many viewed its demise with regret and nostalgia.