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The Keystone LB-13 was the designation given to seven Keystone bombers that were originally to be powered by geared Pratt & Whitney R-1690-3 radial engines. None of the seven aircraft ordered were completed as LB-13s. Five were completed as the Y1B-4, powered by Pratt & Whitney R-1860-7 radials and two as the Y1B-6, powered by Wright R-1820-1 engines. These seven aircraft were completed in 1932.