At its core, the Martin B-10 was a twin-engine, medium-class bomber powered by a pair of Wright R-1820 G-102 "Cyclone" 9-cylinder radial piston engines. The engines were fitted on what would become the USAAC's first attempt at a cantilever low-wing monoplane. The fuselage housed a crew of four that included the pilot and machine gunners. The nose and tail were both glazed over and held defensive armament in the form of machine guns. The aircraft three machine guns in all. A aft section of the fuselage was also glazed over (greenhouse-style) for another crew position and a ventral machine gun was carried near here. All machine guns were of 7.62mm caliber. Internally, the aircraft was cleared to carry upwards of 2,260 pounds of conventional drop ordnance.
After the early B-10 production forms came about, the B-10B (Model 139) followed as primary production versions. These carried R-1820-33 series engines of 775 horsepower (each) and 105 were built to this standard. The B-10M served as a target tug or mail carrier and RB-10MA was a special, modified version of July 1942 flown from Australia to the United States.
YB-12 (Model 139B) arrived as a marginally improved B-10 evaluation model. Over-water safety was improved through installed flotation chambers and Wright engines were given up in favor of 2 x Pratt & Whitney R-1690-11
"Hornet" radials of 775 horsepower (each) instead. Seven of these were produced for April 1940.
B-12A became the first production forms of the YB-12 test models but only 25 units followed to this standard. YB-13 saw PW R-1860-17 "Hornet B" radials of 700 horsepower (each) installed but, despite ten being ordered, none were completed. XB-14 tested PW YR-1830-9 "Twin Wasp" engines of 900 horsepower (each) but only a single YB-12 was converted (and then reverted) for testing. A-15 became a proposed USAAC attack variant but official selection went to the A-14 "Shrike" design offered by competitor Curtiss.
Even while the USAAC began its shift to more modern bomber platforms, export orders (as the "Model 139W") allowed the B-10 lines to remain active for the time being. Customers included the Netherlands with an order of 120, Argentina with 35, and Thailand and Turkey having ordered 26 and 20 respectively.
Aviation engineer Glenn Martin won the prestigious Collier Trophy in 1932 for his design work on the Martin B-10.
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