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The Keystone XLB-3A was the third attempt to produce a twin-engined version of the Huff-Daland LB-1 light bomber. The first had been the Huff-Daland XLB-3, which was effectively a LB-1 but powered by two Liberty engines mounted on the lower wings close to the fuselage. The second was the XLB-5, powered by different Liberty engines, and given a 1926 serial number.
The XLB-3A was a modified version of the original XLB-3. While it was under development Huff-Daland was renamed as Keystone, and the aircraft designation was changed to match. The new XLB-3A was powered by a pair of Pratt & Whitney R-1340 radial engines. It was slightly lighter than the XLB-3, and was 11 mph faster, had a 3,200ft higher service ceiling, and 150 miles better range with a full bomb load.
Both the XLB-3A and XLB-5A adopted the layout that would be standard for all the later Keystone bombers. The nose contained a bombardier’s position at the bottom and a gun position at the top. The pilot’s cockpit was just behind, under the upper wing. At the back of the fuselage was a rear gun position, while the fifth gun fired down through a fuselage tunnel. The tail of the XLB-3A had three vertical stabilisers, compared to the single stabiliser used on the LB-1 and XLB-5.
Engine: Two Pratt & Whitney R-1340 radial engines
Power: 410hp each
Crew: 5
Span: 66ft 6in
Length: 45ft 0in
Height: 16ft 10in
Gross Weight: 11,682lbs
Maximum Speed: 116 mph at sea level
Ceiling: 11,200ft
Range: 550 miles with full bomb load
Guns: Five 0.30in machine guns
Bomb load: 2,200lbs