A Poseidon venture

by Dr. Marshall Michel
86th Airlift Wing historian

***image1***The large percentage of U.S. defense budgets in the late 1940s and early 1950s was allocated to the strategic bombers of the U.S. Air Force, and this drove the U.S. Navy to a number of strategic aircraft programs to wrest some of the budget to their own service.

Its first attempt, the super carrier “United States,” was a victim of interservice rivalry and then budget cuts. So, in 1952 the Navy proposed to create a “Seaplane Striking Force” to be used for both nuclear and conventional warfare, including reconnaissance and mine laying.

A seaplane had the advantage of having a very long “runway” for heavy weight takeoffs, allowing it to carry the very heavy nuclear weapons of that era. The idea was for groups of these seaplanes, supported by a surface tender, to be moved close to Soviet fleet bases in a crisis and where they would be refueled by tanker submarines to mine the Soviet choke points and/or attack the fleet at its base.

The core of the Seaplane Striking Force was to be a striking-looking modern jet seaplane, the Martin P6M “Seamaster,” roughly the equivalent of the Air Force’s B-47 “Stratojet.”

The P6M was huge for a seaplane, with a take-off weight of 160,000 pounds a sharply swept, shoulder-mounted drooped wing with a span of 100 feet and 31 feet high “T“ tail. It carried a crew of four and was powered by four afterburning Allison J-74 turbojets mounted on the top of the wing to prevent ingestion of the water spray, so it could operate in waves up to eight feet high. Its weapons were carried in a watertight rotary bomb bay that flipped over on the bomb run to expose the bomb racks. The Seamaster was designed to “live” in the sea, and all maintenance and weapons loading could be done from the top of the aircraft.

The Seamaster design offered many challenges, specifically how to make a fuselage capable of flight close to Mach 1 while still having good water-handling characteristics. 

The prototype made its first test flight in mid-1955 and exceeded 600 mph in flight tests, but the aircraft suffered from a series of flight control problems not associated with the basic design. In December 1955, the first prototypes had its “T” horizontal stabilizer run away and the P6M pitched down sharply, killing the crew of three – in a serious design oversight, no ejection seats had been fitted.  The second prototype also had a control system failure that sent it into a loop – fatal for such a large aircraft – but, as the aircraft broke up, the crew escaped with a newly fitted escape system.

Despite these problems, the P6M entered production in early 1958. Cost overruns forced a cut in the program from 18 to eight aircraft, and a new class of large aircraft carriers with angled flight with nuclear-capable jet bombers cut into the P6M’s mission. In the event, only three full-up P6Ms were produced and the program was terminated in the autumn of 1959.

Interestingly, Commander Tazwell Sheppard, the officer who was to command the first unit, received a nice consolation prize – in January 1960 he became President John F. Kennedy’s naval aide. (E-mail questions or comments to marshall.michel@ramstein.af.mil)