Keystone Aircraft Corpora¬tion built a total of 220 aircraft in the US Army Air Corps LB (light bombardment) category, venturing briefly also into the B (bombardment) and HB (heavy bombardment) classifications. All except ten of the LBs were twin engined aircraft, but had their origins in the single–engined XLB 1 prototype and nine pre series LB 1 biplanes produced in 1925 by Key¬stone’s predecessor company, Huff Daland and Co Inc of Ogdensburg, New York, which became Keystone in March 1927.
The XLB-1 three-seat, single-engine light bomber was tested in 1923, mount¬ing an 800 hp Packard and was developed as the twin-engined XLB-3, with a crew of five. The basic LB 1 airframe was redesigned by Keystone in 1927 as the twin engined XLB¬3A.
All Aero 