Martin B-10


The Martin B-10 was the first all-metal monoplane bomber to be regularly used by the United States Army Air Corps, entering service in June 1934. It was also the first mass-produced bomber whose performance was superior to that of the Army's pursuit aircraft of the time.
The B-10 served as the airframe for the B-12, B-13, B-14, A-15 and O-45 designations using Pratt & Whitney engines instead of Wright Cyclones.
A total of 348 of all versions were built. The largest users were the US, with 166, and the Netherlands, with 121.

Design and development

The B-10 began a revolution in bomber design. Its all-metal monoplane airframe, along with its features of closed cockpits, rotating gun turrets, retractable landing gear, internal bomb bay, and full engine cowlings, would become the standard for bomber designs worldwide for decades. It made all existing bombers completely obsolete. Martin received the 1932 Collier Trophy for designing the XB-10.
The B-10 began as the Martin Model 123, a private venture by the Glenn L. Martin Company of Baltimore, Maryland. It had a crew of four: pilot, copilot, nose gunner and fuselage gunner. As in previous bombers, the four crew compartments were open, but it had a number of design innovations as well.
These innovations included a deep belly for an internal bomb bay and retractable main landing gear. Its 600 hp Wright SR-1820-E Cyclone engines provided sufficient power. The Model 123 first flew on 16 February 1932 and was delivered for testing to the U.S. Army on 20 March as the XB-907. After testing it was sent back to Martin for redesigning and was rebuilt as the XB-10.
The XB-10 delivered to the Army had major differences from the original aircraft. Where the Model 123 had Townend rings, the XB-10 had full NACA cowlings to decrease drag. It also sported a pair of 675 hp Wright R-1820-19 engines, and an increase in the wingspan, along with an enclosed nose turret. When the XB-10 flew during trials in June, it recorded a speed of 197 mph at 6,000 ft. This was an impressive performance for 1932.
Following the success of the XB-10, a number of changes were made, including reduction to a three-man crew, addition of canopies for all crew positions, and an upgrade to 675 hp engines. The Army ordered 48 of these on 17 January 1933. The first 14 aircraft were designated YB-10 and delivered to Wright Field, starting in November 1933, and used in the Army Air Corps Mail Operation. The production model of the XB-10, the YB-10 was very similar to its prototype.

Operational history

In 1935, the Army ordered an additional 103 aircraft designated B-10B. These had only minor changes from the YB-10. Shipments began in July 1935. B-10Bs served with the 2d Bomb Group at Langley Field, the 9th Bomb Group at Mitchel Field, the 19th Bomb Group at March Field, the 6th Composite Group in the Panama Canal Zone, and the 4th Composite Group in the Philippines. In addition to conventional duties in the bomber role, some modified YB-10s and B-12As were operated for a time on large twin floats for coastal patrol.
In February 1936, the U.S. Army Air Corps used 13 49th Bomb Squadron B-10Bs to drop supplies to the residents of Virginia's Tangier Island and Maryland's Smith Island; with ships unable to reach the islands due to heavy ice in the Chesapeake Bay, the islanders faced starvation after a severe winter storm. The B-10B supply flights followed earlier supply flights to the islands by the Goodyear Blimp Enterprise on 2 February 1936 and by the squadron's Keystone B-6A bombers on 9 and 10 February 1936.
With an advanced performance, the Martin company fully expected that export orders for the B-10 would flood in. The U.S. Army owned the rights to the Model 139 design. Once the Army's orders had been filled in 1936, Martin received permission to export Model 139s, and delivered versions to several air forces. For example, six Model 139Ws were sold to Siam in April 1937, powered by Wright R-1820-G3 Cyclone engines; 20 Model 139Ws were sold to Turkey in September 1937, powered by R-1820-G2 engines.
On 19 May 1938, during the Sino-Japanese War, two Chinese Nationalist Air Force B-10s successfully flew to Japan. However, rather than dropping bombs, the aircraft dropped propaganda leaflets. That followed the project submitted during February 1938. Two French pilots from the 14th International Volunteer Squadron prepared a raid for dropping incendiary bombs over Kagoshima. It was refused.
Dutch Martins fought in the defense of the Dutch East Indies.

Legacy

At the time of its creation, the B-10B was so advanced that General Henry H. Arnold described it as the airpower wonder of its day. It was half again as fast as any biplane bomber, and faster than any contemporary fighter. The B-10 began a revolution in bomber design; it made all existing bombers completely obsolete.
Rapid advances in bomber design in the late 1930s meant that the B-10 was eclipsed by the time the United States entered World War II. The Model 139s in combat in China and South East Asia suffered the same disadvantages as the other early war medium bombers, i.e. not enough armour and guns, while it could not outrun the latest fighters.
An abortive effort to modernize the design, the Martin Model 146, was entered into a USAAC long-distance bomber design competition 1934–1935. The bomber came in a strong 2nd place and was only bested by the Boeing B-17 design in range and endurance. It however had a higher ceiling of 28,500ft and was only 2 mph slower and carried 313 lbs less in bombs than the Boeing at over half the cost. However, the design was seen as a dead end and the 3rd place aircraft Douglas B-18 was selected instead.

Variants

Martin Model 123

Private venture of Martin company, predecessor of the XB-10, served as prototype for the series, one built.
;XB-907
;XB-907A
;XB-10

Martin Model 139, 139A and 139B

Army Air Corps versions, 165 built.
;YB-10
;YB-10A
;B-10
;B-10B
;B-10M
;RB-10MA
;YB-12
;B-12A
;YB-13
;XB-14
;A-15
;YO-45

Model 139W and 166

The export versions, 100 built.
;Model 139WA
;Model 139WAA
;Model 139WAN
;Model 139WC and WC-2
;Model 139WH
;Model 139WR
;Model 139WSM and WSM-2
;Model 139WSP
;Model 139WT
;Model 166
Final version, a.k.a. 139WH-3 and 139WH-3A, 82 built.

Operators

; Siam