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The Martin B-12 was a modified version of the successful B-10, powered by Pratt & Whitney R-1690 Hornet A engines.
The B-10 was the first modern monoplane bomber to enter USAAC service in large numbers. It had a thick mid-mounted wing, with a straight centre section and tapered outer sections. It carried a crew of three or four - a nose gunner in a powered turret, pilot in an enclosed cockpit just in front of the wing and potentially a radio operator and rear gunner in an enclosed cockpit over the rear fuselage. It was armed with three machine guns - one in the nose, one in the rear cockpit and one in the floor under the rear cockpit.
The standard B-10 was powered by the Wright R-1820-33 Cyclone radial engine, with the first production version using a 657hp R-1820-19 engine. Three further versions were ordered, all powered by different Pratt & Whitney engines.
The B-12 was powered by the 775hp Pratt & Whitney R-1690-11 Hornet A, a single row nine cylinder air cooled engine. Two versions were produced, seven YB-12s and twenty-five YB-12As, which could carry an auxiliary fuel tank in the bomb bay for longer ferry flights. This produced a total of 32 B-12s, making it the second most important member of the B-10 family, behind the B-10B.
Some of the B-12s were equipped with twin floats and were used on coastal patrols. In 1935 one of the B-12 floatplanes sent three world payload speed records.
B-10B
Engine: Pratt & Whitney R-1690-11 Hornet A radial engines
Power: 775hp each
Crew: 3 or 4 (nose gunner, pilot, radio operator/ rear gunner)
Span: 70ft 6in
Length: 44ft 9in
Height: 15ft 5in
Guns: Three 0.3in machine guns, in nose and rear turrets and ventral position
Bomb load: 2,260lb