The Martin B-10 was the first of the new generation of monoplane bombers to enter USAAC service in the 1930s, and when it first appeared was a revolutionary aircraft that was faster than the standard fighter aircraft of its day.
The B-10 wasn’t the first monoplane bomber to be examined by the Air Corps. The Douglas B-7 reached the service test stage, although it was very much an intermediate design, with a high mounted wing supported by biplane style struts. The Fokker XB-8 had a thick cantilevered wing, and was produced in 1930 but not accepted for service. The Boeing Y1B-9A was a low wing monoplane bomber which made its maiden flight in 1931, but again only a handful of service test aircraft were ordered.
Work on the Martin B-10 began at the same time as the B-9. The Martin Model 123 was a mid wing monoplane with retractable undercarriage, a crew of three housed in open cockpits and powered by Wright SR-1820E Cyclone engines. It had a thick wing, with a straight centre section and tapered outer panels. The main wheels retracted backwards into the engine nacelles.
This aircraft was officially tested by the Air Corps (as the XB-907) in July 1932, when it reached a top speed of 197mph. This was significantly faster than the B-9, and also outpaced the Air Corp’s fighter aircraft, although not by much - the Boeing P-12 could reach 188mph, and not for long - the Boeing P-26, which made its maiden flight in 1932, could reach speeds of over 230mph, but even so it was almost twice as fast as the previous generation of biplane bombers, which struggled to get much above 100mph.
The Air Corps was impressed with the XB-907, but wanted a number of changes. These including giving it a power operated forward turret, covered with a distinctive glazed dome, increasing the wing span by 8ft 5in and using more powerful 675hp Wright R-1820-19 engines with improved engine cowlings. The prototype was rebuilt to the new standard remarkable quickly, first flying as the XB-907A only four months after its original maiden flight. The modified aircraft was even faster, with a top speed of 207mph, and in January 1933 the Army placed an order for 15 service test aircraft, fourteen as the as the YB-10, using 675hp -25 engines and one YB-10A, with turbo-supercharged R-1820-31 engines. Every aircraft after the prototype had enclosed cockpits, one for the pilot just in front of the wings and one for a radio operator and gunner over the rear fuselage. These last two roles could be carried out by a single crewmember.
One YB-10 was used to evaluate the aircraft's potential as an observation aircraft, as the Martin YO-45, but it wasn't accepted for that role.
Two more B-10s were produced to the same standard as the YB-10, but the main production version was the B-10B, of which 103 were built. This was powered by the 775hp Wright R-1820-33 Cyclone engine, and had a top speed of 213mph. The production versions carried three machine guns - one in the nose turret, one in the rear cockpit and one in the floor below the rear cockpit.
The B-10 was also the basis of three further bombers, each powered by different engines. The B-12 used the Pratt & Whitney R-1690-11 Hornet As. A total of 32 were produced in two variants. The B-13 would have been powered by the Pratt & Whitney R-1860-17 Hornet B. Twelve were planned, but none built. Finally the single B-14 was powered by the Pratt & Whitney R-1830-9 Twin Wasp.
In total 121 B-10s were produced for the USAAC, along with 32 B-12s and 1 B-14, for a total of 154 aircraft based on the original design.
The B-10 entered US service in June 1934. It was used by elements of the 2nd, 6th, 7th and 9th Bombardment Groups in the second half of the 1930s (generally entering service in 1936), but had been retired from front line units by 1940.
One unusual operator was the 1st Pursuit Squadron, which operated a number of B-10s in 1941-41, but this was an experimental unit that served with the Air Forces Proving Ground Group.
It was also used as a target tug, serving with the 14th Tow Target Squadron in 1942-44, and as a home based reconnaissance aircraft with the 105th Reconnaissance Squadron in 1942.
Some were still in American service at the start of the Second World War, although not in front line locations.
The B-10 was also an export success for Martin, with 35 going to Argentina, 9 to China, 118 to the Netherlands, 23 to Thailand, 1 to the Soviet Union and 20 to Turkey, a total of 206 aircraft.
Some of the Dutch aircraft saw combat against the Japanese in the Dutch East Indies. These aircraft included a number of an improved Model 139WH3/ 3A, with more powerful engines and a single enclosed cockpit, but they were all outclassed and all but a handful were destroyed during the desperate attempt to defend the Dutch East Indies.
XB-907/ XB-907B/ XB-10
This was the original prototype, in its two configurations and finally with its USAAC designation.
The YB-10 was the first production version. It was powered by the 675hp R-1820-25 engine. It was the first version to feature enclosed cockpits for all of the crew.
Two further examples of the YB-10 were ordered as the B-10.
The YB-10A was a single prototype that was powered by two 675hp turbo-supercharged R-1820-31 engines.
The B-10B was the main production version. It was powered by the R-1820-33 engine. 103 were built.
The designation B-10M was given to a number of aircraft that were later converted into target tugs.
Engine: Two Wright R-1820-33 Cyclones
Power: 775hp each
Crew: 3 or 4 (nose gunner, pilot, radio operator/ rear gunner)
Span: 70ft 6in
Length: 44ft 9in
Height: 15ft 5in
Empty Weight: 9,681lb
Maximum take-off weight: 16,400lb
Maximum Speed: 213mph
Range: 1,240 miles
Guns: Three 0.3in machine guns, in nose and rear turrets and ventral position
Bomb load: 2,260lb