Martin 275 P6M Seamaster

To meet a US Navy requirement for a high-performance multi-role flying-boat, Martin offered its Model 275 design. This had an all-metal hull of high length/beam ratio, mounting a cantilever high-set sharply-swept wing incorporating so much anhedral that the stabilising floats at the wing-tips could be attached permanently; the tail unit was of T-tail configuration with all-swept surfaces. Above the wing, to minimise spray ingestion, were mounted four Allison turbojet engines, and pressurised accommodation was provided for a crew of five. A beaching cradle allowed the SeaMaster to taxi in and out of the water under its own power. The P6M used a rotary bomb bay (as used on Martin's licence-built Canberras and the XB-51). This permitted weapons release at high speeds without the drag of conventional bomb doors.

The first XP6M-1 prototype was flown on 14 July 1955, the second following on 18 May 1956. Ejection seats were fitted to the second and subsequent aircraft. These proved useful when the second SeaMaster pitched up, went into a loop and disintegrated. The original position of the engine exhausts caused stress on the rear fuselage which resulted in structural damage. The angle of the exhausts was adjusted after testing.

Martin received orders for six pre-production YP6M-1 boats powered by Allison J71 turbojets each developing a maximum 5897kg afterburning thrust. Successful flight testing led to an order for 24 production P6M-2 aircraft named SeaMaster, which differed primarily by having 7711kg thrust non-afterburning Pratt & Whitney J75-P-2 turbojet engines. The cockpit glazing was modified on later models to give a much better overhead and side view. However, the contract was cancelled on 21 August 1959 after only three had been built and these, together with the YP6M-1s, were scrapped at a later date. They were the fastest flying-boats ever built.

YP6M-1
Engines: 4 x J71 turbojet.
Speed: 600 mph.

P6M
Engines: 4 x Pratt & Whitney J75-P-2 turbojets, 7938kg
Wingspan: 30.48 m / 100 ft 0 in
Length: 40.84 m / 133 ft 12 in
Height: 9.45 m / 31 ft 0 in
Max take-off weight: 72575 kg / 160001 lb
Payload: 13600kg / 29983 lb
Max. speed: 965 km/h / 600 mph
Ceiling: 12200 m / 40050 ft
Range: 4830 km / 3001 miles
Armament: 6 x 12.7mm machine-guns, 1800kg of weapons
Crew: 4