During 1944 the US Army Air Force issued its first specification for a large jet bomber. By December 1944 proposals had been received from Boeing, Convair, Martin and North American for medium bomber for tactical- and operational-level use. The Martin Model 223 XB-48 being one of the contenders to meet this requirement.
Two XB-48 prototypes were ordered, the first of them flying on 14 June 1947 as a large shoulder mounted, straight wing monoplane with the capability of carrying up to 9072kg of bombs. Power was provided by six 1701kg thrust Allison J35-A-5 turbo-jets, three mounted beneath each wing. The landing gear was of the new bicycle form with main units ahead of and behind the bomb bay. The 33.02m span Model 223 failed to achieve the performance required and failed to win a production contract.
Engines: 6 x General Electric J35-C-7, 16.7kN
Wingspan: 33.02 m / 108 ft 4 in
Length: 26.14 m / 85 ft 9 in
Wing area: 120.77 sq.m / 1299.96 sq ft
Max take-off weight: 46539 kg / 102601 lb
Empty weight: 26578 kg / 58595 lb
Max. speed: 830 km/h / 516 mph
Armament: 9000kg of bombs