Martin B-10
The Martin B-10 was an all-metal monoplane bomber built by the Glenn L. Martin Company of Baltimore and first flown in 1932. Funded by the company as a private venture, the prototype outpaced the Army Air Corps' biplane fighters at its trials and earned Glenn L. Martin the 1932 Collier Trophy; the type became the Air Corps' standard bomber of the mid-1930s. Exported as the Model 139, it saw combat in Chinese and Dutch service against Japan. One intact example survives, an ex-Argentine Navy aircraft on display at the National Museum of the U.S. Air Force.
Why It Mattered
The Martin B-10 was the first all-metal monoplane bomber that the United States Army Air Corps flew in quantity. The Glenn L. Martin Company built it at its own expense to replace the wood-and-fabric biplane bombers the Air Corps had flown since the First World War. At its Army trials in 1932 the prototype reached 197 mph at 6,000 feet, a speed the Air Corps' biplane fighters of the day could not better. The design earned Glenn L. Martin the 1932 Collier Trophy. Its layout set the pattern the Army's later bombers followed, and it led directly to the medium and heavy bombers flown in the Second World War.
Design Notes
Martin funded the prototype itself and called the design the Model 123; it made its first flight on 16 February 1932. Where contemporary bombers hung their bombs on racks outside the airframe, the Model 123 carried them in a bay inside the fuselage. The airframe was an all-metal monoplane with retractable landing gear, and its two Wright R-1820 Cyclone radials wore low-drag cowling rings of a design produced by the National Advisory Committee for Aeronautics (NACA). The prototype's three crew stations were open, in the manner of the time. Returned to the factory and rebuilt, it gained a longer wing, more powerful Cyclones, full engine cowlings and a hand-turned gun turret in the nose. The first fourteen production machines, the YB-10s, enclosed the cockpit and rear compartment under sliding plexiglass canopies. They carried three Browning .30-calibre machine guns and an internal load of either two 1,130-pound bombs or five 300-pound bombs.
Operational History
The Army bought the rebuilt prototype on 17 January 1933, designated it the XB-10, and ordered 48 production aircraft, which Martin called the Model 139. Deliveries to the USAAC eventually reached 165 aircraft, including 103 B-10Bs; 32 of the first order were built as B-12s, with Pratt & Whitney Hornet engines in place of the Cyclones. B-10s flew from March Field, Langley Field and Mitchel Field in the United States, and served overseas in Hawaii, the Panama Canal Zone and the Philippines. In July 1934, ten B-10s led by Lieutenant Colonel Henry "Hap" Arnold flew from Washington, D.C., to Fairbanks, Alaska, and back, a round trip of more than 7,000 miles. In February 1936 the 49th Bomb Squadron flew thirteen B-10s to drop food and supplies to the icebound island communities of Tangier and Smith Island in Chesapeake Bay. Cleared for export as the Model 139, the bomber went to foreign air forces including China's, Turkey's and the Royal Netherlands East Indies Army Air Force. China's were the first to fight: they bombed Japanese forces in 1937, and on 20 May 1938 two of them dropped leaflets over Nagasaki, a flight Vintage Aviation News records as the first air raid on the Japanese home islands. The Dutch force was the type's largest operator by December 1941, and its Martins defended British Malaya and the East Indies against the Japanese advance, losing most of the fleet in the campaign. The handful of B-10s still in the Philippines were largely destroyed on the ground by Japanese air attacks. At home the type was already leaving front-line service: Martin's own proposed successor, the Model 146, lost the bomber competition to the Douglas DB-1, which entered service as the B-18 Bolo and phased the B-10 out of front-line American units.
Afterlife
Only one complete B-10 survives: the aircraft displayed by the National Museum of the United States Air Force in Dayton, Ohio. It is not a U.S. Army machine but an Argentine Navy Model 139WAN, construction number 715, which reached Argentina in November 1937 and entered service with the serial 0080. It patrolled the Argentine coast through the Second World War, and when its flying ended in 1949, after 1,297.30 hours, it became a teaching airframe at a technical school in Buenos Aires. Argentina transferred the aircraft to the United States in 1970, and by October it had reached the Air Force museum at Dayton. Air Force reservists and civilian volunteers at Kelly Air Force Base in Texas then spent three years restoring it, and in June 1976 it was flown back to Dayton inside a C-5 Galaxy. It now stands in the museum's Early Years Gallery, wearing the serial of the B-10 Arnold flew on the 1934 Alaska flight. Fragments of another Martin survive in the Netherlands: parts of a Dutch 139WH-2, lost on a bombing mission off Bangka Island in February 1942, were found in a mangrove swamp in 1985 and are displayed at the Nationaal Militair Museum in Soesterberg.