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, co-pilot, 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 600Â hp (447Â kW)Â Wright SR-1820-EÂ 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 675Â hp (503Â kW)Â Wright R-1820-19 engines, and 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 197Â mph (317Â km/h) at 6,000Â ft (1,830Â 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.
Variants
Martin Model 123
Private venture of Martin company, predecessor of the XB-10, served as prototype for the series, one built.
XB-907
US Army designation for the Model 123 in evaluation, with open cockpits and two Wright SR-1820-E, delivered April 1932.
XB-907A
Modified XB-907 after Martin returned it to U.S. Army for further operational trials, with larger wingspan and two Wright R-1820-19.
XB-10
Designation of the prototype when purchased by the United States Army Air Corps, Modified XB-907A with enclosed cockpits and turret and single strut landing gear.
Martin Model 139, 139A and 139B
Army Air Corps versions, 165 built.
YB-10
Model 139A, test and production version of the XB-10 with crew reduced to three members, and two 675 hp/503 kW R-1820-25, 14 built, some flown temporarily as float planes.
YB-10A
The YB-10A was different from a YB-10 only in its engines.
It used Wright R-1820-31 turbo-supercharged radials, allowing it to attain speeds of 236 mph (380 km/h).
This made it the fastest aircraft of the B-10 series.
Despite this advantage, only one was built, as a test aircraft.
B-10
According to one source, two additional aircraft ordered in 1936.
B-10B
Model 139, main production version with two 775 hp (578 kW) R-1820-33 engines, 105 built, delivered August 1936.
B-10M
According to one source this was, these were B-10Bs converted as target tugs.
According to Martin’s own archive, this was the designation of the YB-10 after testing, then used for airmail and Alaska missions, 13 of the 14 built were still in service in April 1940.
RB-10MA
One former NEIAF Model 139WH-3A model impressed in July 1942 and flown from Australia to the United States.
YB-12
Model 139B. With 250- or 500-gallons flotation chambers for safety on overwater flights, and two Pratt & Whitney R-1690-11 “Hornet” radial engines.
These 775 hp (578 kW) engines gave similar performance to those on the B-10B (218 mph/351 km/h), seven built, five still in service in April 1940.
(Y)B-12A
The production version of the YB-12 with provision for a 365-gal (1,381 l) fuel tank in the bomb bay, giving the B-12A a combat range of 1,240 mi (1,995 km), 25 built, 23 still in service in April 1940.
YB-13
Re-engined version of the YB-10 powered by two 700 hp (522 kW) Pratt & Whitney R-1860-17 Hornet B radial engines.
Ten were on order but cancelled before production started, not built.
XB-14
To test the new 900 hp Pratt & Whitney YR-1830-9 “Twin Wasp” radial engines, one built which was converted back to YB-12 after testing.
A-15
Proposed attack variant of the YB-10 with two 750 hp (559 kW) R-1820-25 engines, was never built.
The contract fell to the A-14 Shrike.
YO-45
With two 750 hp Wright R-1820-17, proposed high-speed observation role, one B-10 was beginning to be converted in 1934 and another in 1935 but both were stopped before being completed and were converted back into B-10s.
Model 139W and 166
The export versions, 100 built
Model 139WA
Martin demonstrator for Argentina later sold to Argentine Navy.
Model 139WAA
Export version for Argentine Army, 22 built, delivered April 1938.
Model 139WAN
Export version for the Argentine Navy, 12 built, delivered November 1937.
Model 139WC and WC-2
Export version for China, six and three built, delivered in February and August 1937.
Model 139WH
Export version for the Netherlands, used in the Netherlands East Indies.
Produced in block series WH-1(13 built, delivered February 1937)
&
WH-2 (26 built, delivered March 1938)
Model 139WR
Single demonstrator to the Soviet Union.
Model 139WSM & WSM-2
Export version for Siam, three and three built, delivered in March and April 1937.
Model 139WSP
Proposed licence-built version to be built by CASA of Spain, production blocked by U.S. State Department.
Model 139WT
Export version for Turkey, 20 built, delivered September 1937.
Model 166
Final version, a.k.a. 139WH-3 and 139WH-3A, 82 built.
Export version for the Netherlands, used in the Netherlands East Indies.
Redesigned wings, nose and single ‘glass house’ canopy, bomb shackles between engines and fuselage, and better engines.
The WH-3 had two 900 hp (671 kW) R-1820-G5 (40 built, delivered September 1938), the WH-3A had two 1,000 hp (671 kW) R-1820-G-105A (42 built, delivered March 1940).
With the bomb shackles the bomb load could be doubled for a shorter range.
A total of 121 of all types were built for the Dutch.
