propellers. One built. XO-36 Prototype twin-engined observation aircraft. Two direct-drive Curtiss V-1570-23 engines driving two-bladed propellers. Redesignated XB-7. One built. XB-7 Prototype light bomber, with two direct-drive 600 hp V-1570-23 engines driving two bladed propellers. One built. Y1O-35 Service test batch of observation aircraft, powered by V-1570-39 or V-1570-53 engines. Five built. Y1B-7 Service test batch of bombers, powered by V-1570-33 or 675 hp V-1570-53 engines. Seven built. Operators United States Army Air Corps Specifications (Y1B-7) See also References Notes Bibliography Francillon, René J. McDonnell Douglas Aircraft since 1920. London: Putnam, 1979. . Pelletier, Alain J. "Bombers as Postmen: Boeing Y1O-35 and Y1B-7". Air Enthusiast, No. 122, March / April 2006, pp. 30–40. ISSN 0143-5450. Wagner, Ray. American Combat Planes. New York: Doubleday, 1982. . External links Douglas B-7 Douglas B-7 USAAC Fact Sheet: Douglas Y1B-7 B-07 Gull-wing aircraft Douglas B-07 Aircraft first flown in 1931 Twin piston-engined tractor aircraft