The Keystone B-6A Panther was the final development in a series of bombers descended from the Keystone LB-5, and was the last biplane bomber to enter US Army service. The B-6A was the heaviest in the series, although it was only 200lb heavier than the B-4A, and only differed from that aircraft in the use of Wright Cyclone engines in place of the Pratt & Whitney Hornet Bs of the B-4A. The two aircraft had similar performance, although the B-4A had longer range.
The B-6A was otherwise virtually identical to the B-3A, B-4A and B-5A. It was armed with three 0.30in machine guns, one in a nose turret, one in the rear cockpit and one firing down through a fuselage tunnel.
Five Y1B-6s were produced by fitting the Cyclone 9 engines to two LB-13s and three B-3A. The new version of the Panther made its first flight on 28 April 1931. An order was then placed for 39 production aircraft. By the end of the Five Year Program in 1931 the B-4/ B-6 was the Air Corps’ standard bomber.
The B-6A was used during the Army’s experiment in air mail in early 1934, although the bomber aircraft used suffered from some problems with their balance when carrying heavy mail packages in unusual positions. As late as 1935 the 2nd Bombardment Group was still equipped with the type, and as a result did not take part in the December 1935 Air Corps exercises in Florida.
Engine: Wright R-1820-1 Cyclone 9
Span: 74ft 9in
Length: 48ft 10in
Height: 17ft 2in
Gross Weight: 13,374lb
Maximum Speed: 121mph
Climb rate: 690 ft/min
Range: 825 miles
Guns: Three 0.30in Browning machine guns
Bomb load: 2,496lb max, 1,995lb standard