16 February 1932: First flight, Glenn L. Martin Co. Model 123, designated XB-907 by the U. S. Army Air Corps. It was a streamlined all-metal mid-wing monoplane with retractable landing gear. It had an internal bomb bay. The airplane was flown by a single pilot and had two gunners, all in open cockpits.

The Model 123 was a private venture, designed and built at a cost of more than $200,000.

On 26 February 1932, the Model 123 was flown from the Martin plant in Middle River, Maryland, to the Aberdeen Proving Grounds by a U.S. Army Air Corps crew.

The XB-907 was powered by two air-cooled, supercharged 1,823.129-cubic-inch-displacement (29.875 liter) Wright Cyclone SR-1820-E nine-cylinder radial engines, rated at 600 horsepower, each. The engines were covered by Townend rings to reduce drag and improve cooling.

The prototype was tested at Wright Field. The airplane reached a maximum speed of 197 miles per hour (317 kilometers per hour) at 6,000 feet (1,829 meters). Recommendations for modifications were made, and Martin upgraded the prototype to the XB-907A configuration (Martin Model 139), which was then designated XB-10 by the Air Corps, with the serial number 33-139.

Martin increased the XB-907A’s wingspan from 62 feet, 2 inches (18.948 meters) to 70 feet, 7 inches (21.514 meters). The engines were upgraded to Wright R-1820-19s, rated at 675 horsepower. Full NACA cowlings were installed.

The Army then ordered 48 production airplanes.

The XB-907 would be developed into the Martin B-10 bomber.

© 2019, Bryan R. Swopes