In 1930, three Keystone biplane bombers were ordered under the designation LB-14. They were to be equipped with single vertical tails and were to be powered by a pair of 525 hp Pratt & Whitney GR-1860 radials. Shortly thereafter, the USAAC abandoned its separate designation categories for light (LB) and heavy (HB) bombers, and classified them both under the B category. The LB-14s that were ordered were completed under the designation Y1B-5 with 525 hp Wright R-1750-3 engines. They were armed with three 0.30-inch machine guns and could carry 2500 pounds of bombs. Serials were supposedly 30-354 to 30-356, but it is uncertain if these planes were ever actually delivered. In any case, these serials conflict with a batch of serials for the Douglas O-25A.
27 production versions of the Y1B-5 were obtained by converting existing B-3As. These conversions were assigned the designation B-5A. They were powered by a pair of Wright R-1750-3 Cyclone air-cooled radial engines. The Cyclone-engined Keystones could be distinguished from the Hornet-powered Keystones by the presence of the exhaust rings in front on the Cyclones and in the rear on the Hornets.
The B-5A carried a crew of five--pilot, copilot, bombardier, front and rear gunners. Except for the engines, the B-5A was almost identical to the B-3A from which it was converted. The B-5A served with the 72nd Squadron of the 5th Composite Group based at Luke Field in Hawaii. In addition, a training squadron at Kelly Field had a few B-5As.
Specification of the Keystone B-5A:
Two 525 hp Wright R-1750-3 Cyclone air-cooled radial engines. Maximum speed 111 mph at sea level, 106 mph at 5000 feet. Cruising speed 98 mph. Landing speed 57 mph. Service ceiling 10,600 feet. Absolute ceiling 13,000 feet. Weight: 7705 pounds empty, 12,952 pounds gross. Wingspan 74 feet 8 inches, length 48 feet 10 inches, height 15 feet 9 inches, wing area 1145 square feet. Armed with three Browning machine guns, one in each of nose, dorsal, and ventral positions. A bomb load of 2500 pounds could be carried.