The years immediately following World War II were difficult for military aviation. Shrinking defense budgets became a factor driving a number of decisions regarding the procurement of military aircraft. Another aspect of this was a more intense inter-service rivalry between the Navy and Air Force over defense priorities. Defense spending now became a paramount political issue, due to rising cold war tensions. The subject of this blog is a unique aircraft which entered service during this era, however, whose career was short-lived, the Martin Seamaster.
When World War II ended the Army Air Corps (later United States Air Force) B-36 bomber program was already under development. The B-36 was designed as an intercontinental bomber with a combat range of 3,400 miles and a maximum payload of nearly 80,000 lbs. The development of the B-36 dates back to 1941, at which time USAAF planners wanted an aircraft capable of bombing European targets directly from bases in the United States, should Britain fall, the same concept also applied to B-36 missions staged against the Japanese home islands from Hawaii. Once the United States entered World War II, interest in the B-36 began to accelerate, with Secretary Of War Stimson waiving the usual procurement procedures. In July 1943, the USAAF sent a letter of intent to Convair, ordering an initial production run of one-hundred B-36s before the production and testing of two prototype aircraft. The initial delivery date was set for August 1945, however Consolidated, which became Convair in 1943 after the merger with Vultee Aircraft, delayed the first B-36 delivery until August 1946.
The following year, an independent United States Air Force was established. With the Berlin Airlift in 1948, followed by the first atmospheric test of a Soviet atomic bomb in 1949, the US military leadership was forced to consider the most effective means of nuclear delivery from bases in the continental United States to targets in the Soviet Union. Although not capable of aerial refueling, the B-36 was the only aircraft capable of striking Soviet targets with the largest first generation atomic bombs. This appeared to give the Air Force a monopoly on strategic nuclear delivery capability. As result of this, the Navy felt sidelined in the process and sought a means to secure a role in the strategic nuclear delivery mission. The Navy was able to make inroads toward this goal by the Naval Appropriations Act of 1949, approved by President Truman in 1948. The appropriations act provided for the construction of five aircraft carriers built with heavily reinforced armored decks with a displacement of 68,250 tons, approximately one and one-half times that of the Midway Class which came into service at the end of World War II. The lead ship of the class, the USS United States, was designed to accommodate the latest jet bombers and fighters, with a suggested complement of twelve to eighteen bombers with fifty-four jet fighter aircraft. The bombers were to be nuclear capable, carrying a five-ton payload. The United States had a retractable bridge on the right side amidships with four catapults used to launch aircraft, two at the bow and two other units on the outer edge of the deck staggered back. The carrier also had four elevators placed on the outer edges of the deck. At a length of 1,090 ft., the original mission of the United States class was to carry long-range nuclear bombers. During defense budget discussions, testimony was provided by the naval staff, stating that while the United States principal mission was to launch heavy nuclear bombers, the ship would need support from conventional aircraft carriers. The Air Force objected to this point, expressing the view that the cost to operate both the United States and its escorts was more than a comparable bomber wing. Both President Truman and Secretary of Defense Louis Johnson were of the opinion that US defense costs could be controlled by funding the USAF as the only nuclear delivery arm and could trim the defense budget with cuts in the other services. The keel of the USS United States was laid down on April 18, 1949, but construction was stopped five days later due to budget cuts from Secretary Johnson, with the Navy denied a strategic nuclear role.
In an attempt to redress the loss of the USS United States project, the Navy leadership considered another concept that could still give naval aviation a strategic delivery role. The Navy could create a force of nuclear capable seaplanes which would approximate the range and payload necessary for such a mission. These aircraft would be flexible enough to be utilized for conventional missions, such as reconnaissance and minelaying. A requirement was issued in April 1951, calling for a seaplane able to carry a 30,000 pound bombload with a range in excess of 1,500 miles, flown from sea launch bases. Such support vessels would include seaplane tenders and submarines, which could be located close to enemy targets and able to evade detection. The aircraft was to have a low altitude dash speed of nearly 600 mph. Though both Convair and Martin submitted proposals for the seaplane design, the Navy saw more potential in the Martin design, placing an order for two prototypes, followed by six pre-production aircraft with a projected twenty-four production aircraft. The Seamaster was a capable aircraft with four wing-mounted jet engines and could attain a speed of 686 mph. at 20,000 ft. and a cruising speed of 535 mph. It had a combat range of 750 miles with the maximum weapon load of 30,000 lbs. The amphibian had a service ceiling of 50,000 ft. and could carry a variety of weapons to include mines and bombs, in addition to the nuclear role. The first flight of the XP6-M1 (experimental) model of the Seamaster occurred on July 14, 1955. While the flight was a success, subsequent tests revealed the jet engines were mounted too close to the fuselage and scorched it when afterburners were used. This problem was remedied by angling the engines slightly away from the fuselage. However, the following test flight on December 7, 1955 proved tragic as a control system fault with the horizontal tail malfunctioned, causing it to move to the full upward position, causing the airframe to go into a 9 g stress as it began an outside loop, killing all four crew members. Almost a year later, in November 1956, the second Seamaster prototype crashed during a test flight due to a change made in the horizontal stabilizer control, the direct cause of the crash being a faulty elevator jack. The first pre-production Seamaster (YP6M-1), was completed in late 1957 with flight tests resuming in January 1958. The new Seamasters were equipped with the full spectrum of combat equipment and were used for reconnaissance, bombing and mine laying assessments. The J71 jet engines were sometimes unreliable and experienced intake problems with sea water at higher gross weights of the plane.
After the flight tests of the five P6M-1 aircraft were completed in 1958, their replacement, the P6M-2 was introduced in early 1959. The P6M-2 was equipped with more powerful Pratt & Whitney J75 jet engines, improved avionics, an aerial refueling probe, as well as a redesigned canopy with greater visibility. With a few additional modifications, the P6M-2 was an airworthy plane. However, as with the USS United States, the Seamaster was a victim of defense budget cuts by the Eisenhower Administration, with the program ending in August 1959. Perhaps a more important factor in ending the Seamaster program was the advent of the Polaris ballistic missile submarine, which could launch sixteen missiles from under the sea at a range of 1,300 miles. At the time the Seamaster contract was cancelled, it was a state of the art aircraft for its mission, providng the US Navy with a strategic nuclear capability. The aircraft was not obsolete, only its designated mission.