In 1930, seven Keystone bombers were ordered under the designation LB-13. They were to be equipped with single vertical tails and were to be powered by a pair of 525 hp Pratt & Whitney GR-1690 radials. Serials were 30-344/353.
In 1930, the USAAC abandoned its separate designation categories for light (LB) and heavy (HB) bombers, and classified them both under the B category. Of seven LB-13s that had been ordered, five were completed as Y1B-4s with 575 hp Pratt & Whitney R-1860-7 Hornet engines (30-344/348) and the other two were completed as Y1B-6 with 575 hp Wright R-1820-1 Cyclone engines (30-349/350). Three more Wright-powered Y1B-6s (30-351/353) were produced by conversion from production Pratt & Whitney-powered B-3As
On April 28, 1931, the Army ordered 39 B-6A bombers. The B-6A was an improved production version of the Y1B-6. At the same time, the Army ordered 25 B-4As, which were similar but were powered by Pratt & Whitney Hornets. Despite their later sequence number, the Cyclone-powered B-6As were delivered first, being manufactured from August 1931 to January 1932, with the Hornet-powered B-4As being delivered from January to April of 1932. Both the B-4 and the B-6 had three-bladed propellers. The two aircraft could be distinguished from each other by the engine exhaust rings, which were in the front on the Cyclone-powered B-6 and in the rear on the Hornet-powered B-4. The two planes were otherwise almost completely identical.
The B-6A served with the 20th, 49th and 96th Squadrons of the 2nd Bomb Group based at Langley Field, Virginia.
Well over 200 Keystone biplane bombers were built. Only 120 of them served in the continental USA, the remainder being deployed in Hawaii, the Philippines, and in the Canal Zone.
Several Keystone bombers took part in the National Air Races. They also performed as mail carriers during the few months in 1934 when the Army took over the flying of the air mail.
A few B-6As were still in service when World War 2 began, but none saw
any action. They were destined to be the last biplane bombers purchased by the USAAC.
30-349/353 Keystone Y1B-6 32-142/180 Keystone B-6A
Specification of the Keystone B-6A:
Two 575 hp Wright R-1820-7 Cyclone air-cooled radial engines. Maximum speed 121 mph at sea level, 116mph at 5000 feet. 103 mph cruising speed. Landing speed 57 mph. Initial climb rate 690 feet per minute. An altitude of 5000 feet could be reached in 8.6 minutes. Service ceiling 14,100 feet, absolute ceiling 16,500 feet. Range 363 miles with 2500 pounds of bombs, maximum range 855 miles. Weight: 8057 pounds empty, 13,334 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.