||ca. December 1927
The Keystone XLB-3 (originally built under the Huff-Daland name) was a prototype bomber biplane developed in the United States in the late 1920s. It was a twin-engine development of the single-engine LB-1, brought about by a change in policy by the USAAC.
Design and development 
The shift from a nose-mounted engine to engines mounted in nacelles on the lower wing created an opportunity to provide stations for two extra crewmembers: a bombardier and a nose-gunner, bringing the total to five. The LB-1's single tailfin and rudder was augmented by an extra rudder either side of it.
Operational history 
A single prototype was constructed, and delivered to the USAAC for evaluation at the end of 1927. Evaluation, however, showed that performance was actually inferior to that of the single-engine LB-1. The decision was taken to change the XLB-3's water-cooled Liberty engines for air-cooled radials, at which point it was redesignated XLB-3A. With performance still unsatisfactory, development was abandoned in favor of a parallel design, the LB-5.
Specifications (XLB-3A) 
Data from Jane's Encyclopedia of Aviation
- Crew: Five - pilot, copilot, bombardier, two gunners
- Length: 45 ft 0 in (13.72 m)
- Wingspan: 67 ft 0 in (20.42 m)
- Height: 16 ft 10 in (5.13 m)
- Wing area: 105.8 ft2 (1,038 m2)
- Empty weight: 6,065 lb (2,756 kg)
- Gross weight: 11,682 lb (5,310 kg)
- Powerplant: 2 × Pratt & Whitney R-1340, 410 hp (305 kW) each
- Maximum speed: 116 mph (186 km/h)
- Range: 544 miles (870 km)
- Service ceiling: 11,210 ft (3,400 m)
- Rate of climb: 550 ft/min (2.8 m/s)
- 2 × trainable .303 in (7.7 mm) Lewis guns in open position in nose
- 2 × trainable .303 in (7.7 mm) Lewis guns in open dorsal position
- 1 × trainable .303 in (7.7 mm) Lewis gun in ventral hatch
- 2,205 lb (1,000 kg) of bombs
- Taylor, Michael J. H. Jane's Encyclopedia of Aviation. London: Studio Editions, 1989.
- World Aircraft Information Files. London: Bright Star Publishing, File 899, Sheet 09.