To meet a US Navy requirement for a high-performance multi-role flying-boat, the company offered its very advanced Martin 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 anhe-dral that the stabilising floats at the wirwg-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. The first XP6M-1 prototype was flown on 14 July 1955, the second following on 18 May 1956, and 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. 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.