When the Army Air Corps requested proposals for a twin-engine attack bomber capable of flying 1,200 miles at 200 mph with 1,200 pounds of bombs, Martin submitted a design with company model number 167. The Martin design competed against designs by Douglas, Stearman, North American and Bell. After evaluating the proposals, the Air Corps rejected all of them and asked for revised designs. Bell dropped out of the competition, but the other four proposals were accepted and the Air Corps asked for prototypes to be built at company expense. Martin completed the Model 167 prototype in early 1939 and it was flown to Wright Field in Dayton, Ohio for testing in March.
The aircraft featured Pratt & Whitney R-1830 Cyclone radial engines, a maximum bomb load of 1,800 pounds, and a dorsal turret which retracted into the fuselage when not in use. The Model 167, with a crew of three: pilot, bombardier and gunner, could fly at a top speed of 280 mph and met the Air Corps requirement of a 1,200-mile range at 200 mph with 1,200 pounds of bombs.
The Army tested the Martin Model 167 with the civil registration NX22076, but eventually purchased it and designated it: XA-22. The XA-22 never entered production; however, France ordered 115 export models, 167F, in January 1939. When France fell in mid-1940, the remaining Model 167Fs were diverted to Great Britain. The RAF ordered its own version under the designations Maryland Mk. I and Mk. II.
Attack bomber prototype
TECHNICAL NOTES: Armament: Provisions for four wing-mounted .30-cal. machine guns, one ventral .30-cal. machine gun and one .30-cal. machine gun in a retractable dorsal turret plus 1,800 lbs. of bombs Engines: Two Pratt & Whitney R-1830-37 radials of 1200 hp. each at takeoff power Maximum speed: 280 mph Cruising speed: 260 mph Combat range: 750 miles with 1,800 lbs. of bombs Maximum range: 1,900 miles Service ceiling: 20,000 ft. Span: 61 ft. 4 in. Length: 46 ft. 8 in. Height: 10 ft. 0 in. Weight: Approx. 17,000 lbs. gross weight Crew: Three (pilot, bombardier and radio operator/gunner) Serial number: 40-706; Martin Model 167; civilian registration NX22076