Editing Martin P4M Mercator (section)

==Design and development==
Work began on the Model 219 in 1944, as a replacement for the [[Consolidated PB4Y Privateer|PB4Y Privateer]] long-range patrol bomber, optimised for long range minelaying missions, with the first flight being on 20 October 1946.<ref name="WoF p139">Lake and Dorr 2000, p.139.</ref> A large and complicated aircraft, it was powered by two [[Pratt & Whitney]] [[Pratt & Whitney Wasp Major|R4360 Wasp Major]] 28-cylinder [[radial engine]]s. To give a boost during takeoff and combat, two [[Allison J33]] turbojets were fitted in the rear of the two enlarged engine nacelles, the intakes being beneath and behind the radial engines.<ref name="WoF p138-9">Lake and Dorr 2000, pp. 138–139.</ref> The jets, like those on most other piston/jet hybrids, burned gasoline instead of jet fuel which eliminated the need for separate fuel tanks.

A [[tricycle undercarriage]] was fitted, with the nosewheel retracting forwards. The single-wheel main legs retracted into coverless fairings in the wings, so that the sides of the wheels could be seen even when retracted. The wings themselves, unusually, had a different airfoil cross-section on the inner wings than the outer.

Heavy defensive armament was fitted, with two 20&nbsp;mm (.79&nbsp;in) cannon in an Emerson nose turret and a Martin tail turret, and two 0.5&nbsp;in (12.7&nbsp;mm) machine guns in a Martin dorsal turret. The bomb bay was, like British practice, long and shallow rather than the short and deep bay popular in American bombers. This gave greater flexibility in payload, including long torpedoes, bombs, mines, depth charges or extended-range fuel tanks.<ref name="Ferret 216-7">Dorr and Burgess 1993, pp. 216–217.</ref>