|B-10 being flown during a training session at Maxwell Field|
|Manufacturer||Glenn L. Martin Company|
|Designer||Peyton M. Magruder|
|First flight||16 February 1932|
|Retired||1949 Royal Thai Air Force|
|Primary users||United States Army Air Corps|
Netherlands East Indies AF
Turkish Air Force
|Number built||121 B-10|
82 model 166
348 of all variants including 182 export versions
|Variants||Martin Model 146|
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.
The B-10 began a revolution in bomber design. Its all-metal monoplane airframe, along with its features of closed cockpits, rotating gun turrets (almost simultaneously with the 1933 British Boulton & Paul Overstrand biplane bomber's own enclosed nose-turret), retractable landing gear, internal bomb bay, and full engine cowlings, became 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 (447 kW) 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 (503 kW) Wright R-1820-19 engines, and an 8 feet (2.4 m) 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 (317 km/h) at 6,000 ft (1,830 m). 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 (503 kW) 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.
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 US Army Air Corps used 13 B-10Bs of the 49th Bomb Squadron 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 its 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 25 August 1937, as the air battles intensified in the early part of the Second Sino-Japanese War, five Chinese Nationalist Air Force bombers of the 8th BG, 19th and 30th Squadrons consisting of three Heinkel He-111As and two Martin B-10s respectively, flying from their base in Nanjing to Shanghai, successfully dropped their bombs on Japanese landing forces at Liuhe, Taicang northwest of Shanghai, however Japanese aircraft pursued the bombers and shot up two of the Heinkels, forcing them to crash land; two crew members were killed on the ground by Japanese aircraft strafing at them.
As the National Revolutionary Army of China fought desperately to hold onto their remaining positions in the Battle of Shanghai, the Chinese Air Force launched a major strike with a motley mix of aircraft against Japanese positions in Shanghai on 14 October 1937, consisting of three B-10s, two Heinkel He-111As, five Douglas O-2MCs, five Northrop Gammas, and three Curtiss Hawk IIIs from Nanjing in the late afternoon; in the evening, one bomber was launched every hour from Nanjing to attack Japanese positions in Shanghai until 03:00 on 15 October.
On 19 May 1938, two B-10s of the 2nd BG, 14th Squadron, led by Capt. Hsu Huan-sheng and Lt. Teng Yen-bo, successfully flew a nighttime "raid" over Japan. However, rather than dropping bombs, the B-10s dropped 2,000,000 leaflets, "alerting the conscience of the Japanese people against atrocities committed by the Japanese invasion and occupation of China", over the cities of Nagasaki, Fukuoka, Kurume, Saga, and others, while reconnoitering airbases, ports, warships and factories.
In the mid 1930s, the Netherlands government adopted a doctrine for defense of the Netherlands East Indies which placed reliance on the use of land-based bombers against any attacking force, with orders for defensive fighters cancelled to pay for the bomber force. The Martin 139 was chosen in preference to the Dutch Fokker T.V, as its all metal construction was considered more robust than the steel tube and fabric Fokker, while the Martin bomber was already in production and therefore would be available quicker. Twelve Martin 139 WH-1s were ordered for the Royal Netherlands East Indies Army Air Force in 1936, followed by 26 improved WH-2s in March 1937, sufficient bombers to equip a Group of three squadrons. In December 1937, an order was placed for 39 Martin 139 WH-3s, followed by an order for 40 Martin 139 WH-3As in November 1938. Two more Martin 139 WH-3As were ordered in July 1939 to replace aircraft lost during delivery. The last of these attrition replacement aircraft was delivered in March 1940 as the last Martin B-10/139 built. On the outbreak of war with Japan in December 1941, about 58 Martins (WH-3 and WH-3As) were operational with six squadrons, with about 20 more of the older variants in reserve. B-10s of the Royal Netherlands East Indies Army Air Force served in the defense of the Dutch East Indies.
Six B-10s formed the medium bomber force of the Royal Thai Air Force at the start of the 1940–1941 Franco-Thai War. They flew several bombing missions during the war, with their first mission against Xieng Khuang, Laos and a nearby airfield on 15 December 1940, with the last mission, against Sisophon in what is now Cambodia on 28 January at the very end of the Franco-Thai War.
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 in 1934–5. The bomber came in a strong second place and was only bested by the Boeing B-17 in range and endurance. However, it had a higher ceiling of 28,500 ft (8,700 m) and was only 2 mph (3 km/h) slower and carried 313 lb (142 kg) less in bombs than the Boeing at over half the cost. Nonetheless, the design was seen as a dead end, and the third-place contender, the Douglas B-18, was selected instead.
Private venture of Martin company, predecessor of the XB-10, served as prototype for the series, one built.
Army Air Corps versions, 165 built.
The export versions, 100 built (182 including the Model 166, see below).
Final version, a.k.a. 139WH-3 and 139WH-3A, 82 built.
Data from United States Military Aircraft Since 1909.