On 23 August 1938 the US Navy ordered from Martin a single prototype of the Martin 170 design for a patrol bomber of flying-boat configuration. Designated XPB2M-1, it was the world's largest flying-boat when flown for the first time on 3 July 1942, but by then the United States had become involved in World War II and it was decided not to proceed with procurement of the type as a patrol bomber. Instead, the boat was modified for use in a transport role, becoming re-designated XPB2M-1R and entering service in December 1943. It remains the largest flying-boat to have been operated by the US Navy and an early demonstration of its capability came in 1944, when a 9299kg cargo was delivered to Hawaii in a 7564km round trip completed in only 27 hours 36 minutes, resulting in a US Navy order for a production version under the designation JRM-1 Mars. This covered 20 aircraft to be completed specially for the transport role, but the end of World War II brought contract cancellations and only five were built, plus a single JRM-2 for operation at a higher gross weight. When the five JRM-1s were later modified to this latter standard they became redesignated JRM-3. These 60.96m span aircraft were powered by four 1715kW Wright R-3350-8 engines, and an appreciation of their capacity can be gained from the fact that on 19 May one of them, Marshall Mars, carried a total of 301 passengers, plus its crew of seven.

3-View

A three-view drawing (684 x 776)