Air Power
MARTIN B-10
The B-10, the first of the "modern-day" all-metal monoplane bombers to be produced in quantity, featured such innovations as internal bomb storage, retractable landing gear, a rotating gun turret, and enclosed cockpits. It was so advanced in design that it was 50% faster than its contemporary biplane bombers and as fast as most of the fighters. When the Air Corps ordered 121 B-10s in the 1933-1936 period, it was the largest procurement of bomber aircraft since WW I. It also ordered 32 B-10 type bombers with Pratt and Whitney rather than Wright engines and designated these B-12s.
General Henry H. "Hap" Arnold once called the B-10 the air power wonder of its day. In 1934, he led ten B-10s on a 8,290 mile flight from Washington, D.C. to Fairbanks, Alaska and back. Although Air Corps B-10s and B-12s were replaced by B-17s and B-18s in the late 1930s, China and the Netherlands flew export versions in combat against Japan.
Like the MB's during the 1920's, the Martin B-10 series set the standard for land-based bombers for a decade - during which "Martin Bomber" described a whole generation of aircraft types. Its design marked the first successful military application of the new airframe technology of the 1930's - streamlined monocoque fuselage, variable-pitch propellers, and thick metal wings with lift-enhancing flaps, integral fuel tanks, and retractable landing gear.
Martin developed the B-10 in response to an Air Corps design directive issued late in 1929 for an advanced bomber. The response was highly competitive, and victory did not come easily. Fokker, Keystone, Douglas, Ford, and Boeing all submitted designs and prototypes before Martin. Martin's first submission actually stated the company's preference for another biplane bomber. It was summarily rejected by the Air Corps' Materiel Division, which responded with a series of specific suggestions for improvement that continued throughout the development of the design. After wind tunnel tests in 1931, Martin gambled on a prototype Model 123, built at its own expense and finished in February 1932. Powered by Wright R-1820 Cyclone engines, it could fly at 197 mph, making it faster than the competing planes. Designated XB-907, the prototype was then tested at Wright Field, which had replaced McCook as the Army's air testing center. Found to suffer from engine vibration, instability in flight, and an excessive landing speed of 91 mph, back it went to the Martin plant with still another list of suggestions from the Materiel Division.
By this time the success of the new design had become vital to Martin's corporate survival. Navy contracts were running out, and the financing for the new factory in Middle River was in disarray. Martin had planned to float a stock issue in 1929, but the Great Crash came first, leaving the company debt in the form of high-interest gold bonds due to mature in 1936. The company eventually had to seek temporary help from the Reconstruction Finance Corporation; in the meantime Glenn Martin developed anemia and an ulcer worrying about how to meet payroll and interest payments. The company business manager, C.A. Van Dusen, had by this time succeeded Bell as second in command. He persuaded Martin to take a vacation while he and chief engineer Milburn made a determined effort to satisfy the Materiel Division. They gave the prototype longer wings, now made integral with the center section of the fuselage, and mounted more powerful Cyclone engines in the new streamlined NACA cowlings. The landing gear was modified, and an innovative glazed turret was developed to assist the nose gunner in traversing his gun against the airstream. By October 1932 the XB-907A was ready; it scored a triumphant success at Wright Field. Clocked at 207 mph with full load, not only was it faster than the competing Boeing XB-9 and Douglas XB-7, but it matched the speed of the newest pursuit planes in the Air Corps inventory.
In January 1933 the Army contracted for 48 planes costing almost $2.5 million. It was a complicated order. Besides the prototype XB-907A, now designated XB-10, the Army would receive 13 similar YB-10's (the prefix indicated a service-test model) plus a single YB-10A for testing with supercharged Wright engines. Seven YB-12's would be built for testing with Pratt and Whitney R-1690 Hornet engines, to be followed by 25 regular-service B-12A's with the same engines but fitted up with extra fuel tanks and flotation chambers for overwater flying. (The Air Corps had recently taken over part of the nation's coast-defense mission.) Finally, an experimental XB-14 would be tested with new Pratt and Whitney R-1830 Twin Wasp radials.
Besides the big contract, Glenn Martin was summoned to the White House in March 1933 to receive the Collier Trophy for aviation achievement. His response to President Roosevelt, accepting the honor on behalf of "everyone who worked on the design and who helped rivet it together" enraged the Air Corps Materiel Division engineers. They prepared an eight-page memorandum insisting that Martin should have stated that he owed it all to them.
The YB-10's and YB-12's delivered to the Air Corps early in 1934 were to have an unusual course of testing. Alleging corruption, Postmaster General Jim Farley had just cancelled all air mail contracts; the Air Corps was ordered to fly the mail. Results were generally disastrous in terms of pilot fatalities and cancelled service. The big, fast, fully instrumented bombers were eagerly pressed into service. They proved to be a godsend, improving reliability and safety simultaneously. Once the air mail was put back in civilian hands, Air Corps leaders sought to counter the bad publicity by a dramatic demonstration of competence in the air. They hit upon a massed flight of YB-10's from Washington, D.C., to Alaska. The planes would carry cameras to map the wilderness, and their appearance on the North American frontier would impress both the Japanese and the U.S. Navy, which had just completed a mission there with Martin PM-1 patrol planes. Colonel Henry "Hap" Arnold was chosen as flight commander; during July and August 1934 he managed to bring all ten planes through the arduous 18,000-mile mission.
After these successes Martin had every reason to expect another large order. What with all the various experimental and service-test versions the company had designed and produced, it made sense to regard Martin as a sole source. When the Army nevertheless discussed letting competitive bids in early 1934, Martin countered by requesting permission to sell the Air Corps' newest bomber to Soviet Russia, Brazil, and China. A Russian attempt to purchase 20 PM-1's in 1930 had been rebuffed by the State Department due to the Soviets' "definite policy of world revolution." Once again, Martin was refused permission to export, but did receive a huge order from the $7.5 million in Public Works funds voted by Congress in the spring of 1934. Contracts for 103 planes were spread over fiscal years 1934 and 1935. They were all the definitive B-10B version with Wright R-1820-33 engines.
B-10's served in every bombardment group in the Air Corps during the 1930's. As fast as contemporary pursuit planes, they proved nearly unstoppable in Army maneuvers. In 1935 they carried out the first Army tests of the Navy's Norden precision bombsight, and their success confirmed Air Corps strategists in their expectation that daylight precision bombing could be effective even beyond the range of escort fighters. Ironically this stimulated the development of larger, longer-range bombers that superseded the B-10 - in particular the Boeing B-17 Flying Fortress.
By 1936 the Air Corps was losing interest in the B-10 as a bomber. A few were tested as attack and observation planes, designated A-15 and O-45. Some thought was even given to a heavy fighter version. Although there were a number of disputes with Martin over design and construction defects in the B-10 series, 119 of the 151 planes purchased 1932-35 were still in service in the spring of 1940. Most were assigned to target-tow and training duties as B-10M's and B-12AM's, though seventeen planes in the Philippines were still in combat status.
In 1936 the Martin 139 design was released for export, and the company did a booming business, eventually selling 189 planes abroad. The Soviets were first in line, purchasing a single plane and blueprints in the summer of 1936. They were followed by the Netherlands East Indies, China, Siam, Argentina, and Turkey. The Dutch were the best customers, buying 120 planes in four different versions for the defense of their rich Indonesian colonies. Influenced by bomber advocates who saw the 139's as ultimate weapons, they did not purchase modern fighters.
Foreign orders for Model 139 kept the Martin factory busy until 1939. Many of the planes were busy too. Chinese 139WC's raided Japan in 1938, though at a range of 2,500 miles they could drop only leaflets. Siamese 139WSM's flew against both the French and the Japanese. The Dutch bomber fleet flew gallant but nearly suicidal unescorted missions against the Japanese invaders in 1941 and early 1942. As Java fell in March 1942, a bullet-riddled 139WH-2 overloaded with fourteen Dutch officers and officials managed to stagger from Bandung to Australia. It was subsequently impressed into the U.S. Army Air Forces there, receiving U.S. serial 42-68358 and the Busby Berkleyesque nickname "Miss Latrine of 1930." Other Dutch 139's, captured by the Japanese, eventually were handed over to Siam, now Japan's ally. The planes served until the late 1940's there and in Turkey, and even later in Argentina. One of the Argentine Martins is the only survivor of the type. Restored to prewar Air Corps colors it is on display at the U.S. Air Force Museum at Wright-Patterson Air Force Base.
SPECIFICATIONS
Span: 70 ft. 6 in.
Length: 44 ft. 9 in.
Height: 15 ft. 5 in.
Weight: 14,700 lbs. loaded
Armament: Three .30-cal. machine guns, 2,200 lbs. of bombs
Engine: Two Wright R-1820's of 775 hp. each
Cost: $55,000
PERFORMANCE
Maximum speed: 215 mph.
Cruising speed: 183 mph.
Range: 1,370 miles
Service Ceiling: 24,000 ft.
