The Keystone B-3A Panther was the fourth version of the Keystone bomber to be produced in significant numbers, and the first to receive a designation in the new B (bombardment) sequence, adopted by the Army Air Corps in 1926.
The B-3A was originally ordered as the LB-10A. The only LB-10 to be built had been powered by Wright engines, but for the B-3A the engines were changed to Pratt & Whitney R-1690-3s of the same power. The B-3 had the same single rudder tail as the LB-10, differing from the earlier entries in the LB series, which had twin or even triple vertical control surfaces on the tail. The B-3A was more lightly armed than the LB aircraft, carrying three guns in place of their five – one in the nose, one in the rear cockpit and one in a fuselage tunnel.
The B-3A was a conventionally constructed biplane, fabric covered over a framework of steel tubes. It had almost twice the range of the LB-10, but was otherwise similar.
Of the 63 B-3As originally ordered, 36 were delivered to the Army Air Corps, while the final 27 were completed as the B-5A. Three of the B-3As were used to produce the service test Y1B-6s.
Thirty one of the B-3As had been delivered in time to take part in the 1931 manoeuvres, where they operated alongside nine Curtiss B-2s and four remaining LB-7s. By the mid 1930s the Panther was obsolete, and the few remaining in use on the Continental United States were serving with observation units, but they remained in use on overseas stations much longer. The last B-3As were withdrawn from the 2nd Observation Squadron on the Philippines in 1940.
Engine: Pratt & Whitney R-1690-3
Span: 74ft 9in
Length: 48ft 10in
Height: 15ft 9in
Empty Weight: 7,705lb
Gross Weight: 12,952lb
Maximum Speed: 114mph, 102mph at 5,000ft (operating altitude)
Cruising Speed: 76mph or 98mph
Climb rate: 650ft/min
Range: 860 miles with full bomb load
Radius of Action: 382 miles
Guns: Three 0.30in Browning machine guns
Bomb load: 2,496lb max, 1,995lb standard