An unprecedented long-range mission and a severe test for the Air Corps’ new B-10 bomber was made in the summer of 1934, when Lt. Colonel Henry H. Arnold led ten of the Martin bombers on a grueling 7,360-mile round-trip flight from Washington, D. C, to Alaska and return. The airplanes left Washington on July 19th with orders to photograph strategic landing sites, to determine the usefulness of a major air force in Alaska in time of emergency, and to prepare on over-all report on northern frontier defenses. En route to Alaska the bombers made refueling and supply stops at Patterson Field, then at Minneapolis, Winnipeg, Regina, Edmonton, Prince George and Whitehead, arriving July 24th at Fairbanks. From this base the planes photographed 20,000 square miles – a strip 400 miles long and 50 miles wide – mapping airways in and out of Russia, and from across the Arctic Circle. The only accident occurred on August 3rd when a bomber sank during a forced landing in Cook Inlet; the crew escaped without injury and a week later the plane was flying again. The other B-10s flew home nonstop from Juneau to Seattle.
A flight of B-10B bombers, the primary service version, during a bombing exercise. The type remained dominant in the Air Corps throughout the second half of the 1930s.
A Martin B-12 at March Field, California, in November 1935. A derivative of the B-10, this version had additional fuel tanks on the fuselage for long range duties.
The two outstanding models in the 1930 heavy bomber competition were the Boeing B-9 and the Martin B-10. The Boeing entry, an all-metal, low-wing monoplane of clean design, was delivered first for test flight. Pilots were enthusiastic about its excellent handling characteristics, and nothing less than exuberant about its speed of 186 miles per hour at 6,000 feet—some 60 miles per hour faster than any existing service bomber in the world. Engineers noted that the “quantum jump” of one-third more speed came not from increased horsepower, but through structural refinements and aerodynamic efficiency of the monoplane design, as well as a reduction in drag resulting from a retractable landing gear.
But if the Boeing B-9 was outstanding, the Martin B-10 of the same competition was all that, and more. Its performance exceeded even that of the Boeing monoplane bomber, and pilots said of the Martin that “it looked, as well as acted, the part of a modern bomber.”
In the early 1930s, officials in the U. S. Army Air Corps contracted with the Glenn L. Martin Company of Baltimore to build a series of twin-engine, all-metal bombers with retractable landing gear. The resulting B-10/B-12 became the first modern bombers in the USAAC operational inventory. Faster than any fighters, they helped develop theories of unescorted precision daylight strategic bombing then germinating among U. S. airmen. The fuselage housed a crew of four that included the pilot and machine gunners. The nose and tail were both glazed over and held defensive armament in the form of machine guns. The aft section of the fuselage was also glazed over (greenhouse-style) and included a ventral machine gun.
The prototype Model 123 first flew on 16 February 1932. Designated the XB-907, it reached speeds of 197 mph during July trials at Wright Field, Ohio. That fall it was returned to Martin for minor upgrades.
Following successful trials in October, the Army purchased the bomber on 17 January 1933 and designated it the XB-10. Army officials also ordered 48 production aircraft. The first 14 were YB-10s and had 675-hp Wright R-1820-25 engines. The YB-10s had transparent sliding canopies over the pilot’s cockpit and over the rear gunner’s position.
Martin completed delivery of 103 aircraft in August 1936. The B-10B had two Wright R-1820-33 775-hp engines. With a 71-foot wingspan and 45-foot length, it stood 15 feet high. Its gross weight was 16,400 pounds with a service ceiling of 24,200 feet and a range of 1,240 miles. Top speed was 213 mph, and it carried a bombload of 2,260 pounds.
The B-10/B-12s were popular among USAAC crews and a great success for Martin. In late 1932, Glenn L. Martin won the 1932 Collier Trophy for building the B-10.
The B-12As were powered by Pratt and Whitney R-1690- 11 Hornet radial engines. The B-12, with its greater fuel capacity and ability to be fitted with large twin floats, took on the role of coastal defense. In the late 1930s, the B-10/B-12s were generally replaced by Douglas B-18 Bolos and more modern four-engine Boeing B-17s.
Like the Boeing, the mid-wing Martin was a superb aerodynamic design. Unlike the Boeing, it had enclosed crew compartments and an enclosed turret in the nose. When tested in 1932, the Martin showed a speed of 207 miles per hour and a ceiling of 21,000 feet, performance that rated it as the fastest and most powerful bomber in the world. With these two planes the United States had forged a lead in bombardment weapons that was never to be relinquished.
To the proponents of strategic airpower the Boeing and Martin twin-engine bombers not only established new standards of performance and design, but once and for all removed the obstacles to truly long-range, high-speed bomber operations that still waited for fruition. It was not to be long in coming, and, notes the Air University, it was in 1932 that:
the Materiel Division took steps to improve all heavy bomber equipment. Emphasis was placed on monoplane design, all-metal construction, and streamlining; the transition from wood-and-fabric to metal was virtually complete by 1935. Even more significant, however, was the consequence of the success of these new bombers upon the development of larger aircraft. Supporters of the strategic bombardment idea had always seen the desirability of large planes, since both range and load are primarily a function of size. However, until this time it had been believed that size mitigated against speed. Development of the B-9 and B-10 demonstrated that aerodynamic efficiency could be increased with size, thereby providing an open sesame for development of bigger and faster bombers.
That “open sesame” was soon established to be, not the fanciful remark of the airpower enthusiasts, but a trend that would swiftly bear its fruit. The mass production of the B-10 graduated an engineering breakthrough to the practical and widespread application of the “new airpower.” But there was more to come, and Air Corps leaders were quick to exploit the breakthrough.
On November 27, 1933 the Army accepted delivery of its first production-model Martin B-10, the nation’s first all-metal monoplane bomber produced in quantity. The twin-engine airplane featured an internal bomb bay, retractable landing gear, rotating gun turret, and enclosed cockpit. A precursor of World War II bombers, the B-10 could fly faster than contemporary pursuit aircraft and much faster than previous biplane and triplane bombers.
The Martin B-10 had flight controls in the rear . There was a folding seat that when locked into position elevated the gunner or radio operator about the same height as the pilot up front. The control column, rudder pedals and throttles had to be used from the seat. It is doubtful anyone tried to fly the aircraft from this position.
Lt. Col. Henry H. Arnold and 10 Martin B-10 bomber crews completed a month-long air trip of more than 7,000 miles from Bolling Field, Washington, D.C., to Fairbanks, Alaska, and back on August 20, 1934.
In August 1936, versions of the B-10 were demonstrated for foreign sale. Argentina bought 39 in 1936 and China bought six in 1937. The Soviet Union bought one, Siam (Thailand) bought six, and Turkey in 1937. Between September 1936 and May 1939, the Dutch bought 117 of the most modern versions for use in the East Indies. These saw combat against invading Japanese in the early 1940s. Between 1933 and 1939, 189 export and 153 USAAC B-10/B-12/B-14s were produced and delivered. The only remaining B-10 was donated by the Argentine government to the U. S. government for display in the U. S. Air Force Museum in 1970. An export version, it was refurbished as a USAAC B-10B. It went on display in 1976.
A unique mission in April 1938 saw two Chinese Martin B-10 bombers fly a mission over Japan, but dropping only anti-war leaflets over the Japanese cities of Nagasaki and Saga.
By the beginning of WWII the Royal Siamese Air Force more often had to make do with outdated equipment. Recently turned obsolete was the formerly cutting-edge Martin B-10, enabled by its twin, 755-hp Wright R-182033 (G-102) Cyclone radial engines to outrun every pursuit plane at 213 mph when introduced in 1934, since overtaken by interceptor development, but still capable of carrying 2,260 pounds of bombs. Siam’s Royal Air Force received six of these rapidly aging medium-bombers in 1937.
The Philippine Army Air Corps were even given three (3) Martin B-10 Bombers just before the war.
Model 123, 139 and 166, B-10, -12 and -14
Origin: The Glenn L. Martin Company Type: 4/5-seat medium bomber.
Engines: (YB-10) two 775hp Wright R-1820-25 Cyclone nine-cylinder radials: (YB-12) two 665hp Pratt & Whitney R-1 690-11 Hornet nine-cylinder radials. (XB-14) two 850hp P&W R-1 830-9 Twin Wasp 14-cylinder two-row radials: (most export 139) 750hp Cyclone SGR-1820- F3S. (export 166) usually 850hp Cyclone R-1820-G2, but some 900hp Twin Wasp R-1 830-SC3-G.
Dimensions: Span 70ft 6in (21 48m): length 44ft 8in (13.63m): (XB-10) 45ft; (B-12A) 45ft 3in: (export 166) 44ft 2in; height 11ft (3.35m); (XB-10) 10ft 4in. (B-10B) 15ft 5in. (export 166) 11ft 7in
Weights: Empty (typical B-10. 139) 8.870-9.000lb: (166) 10,900lb (4944kg); maximum loaded (XB-10) 12,560lb; (B-10B) 14,600lb (6622kg); (B-12A) 14,200lb. (139) 14,192lb. (166) 15,624lb (Cyclone) or 16,100lb (Twin Wasp).
Performance: Maximum speed (all B-10. 139. B-12) 207-213mph (340km/h); (166) 255mph or 268mph (P&W): initial climb (all) 1,290-1,455ft (about 410m)/min: service ceiling (all) 24,200-25,200ft (about 500m): range with bomb load (typical) 700 miles (1125km). maximum range with extra fuel (early models) 1,240 miles. (166) 2,080 miles
Armament: (All) three rifle-calibre (usually 03in) machine guns manually aimed from nose turret, rear cockpit and rear ventral hatch; bomb load of 1,000lb (454kg) in internal bay beneath centre section in fuselage.
History: First flight (Model 123) January 1932; service delivery (123) 20 March 1932: (YB-10) June 1934; (export 139) late 1935; (166) January 1938 Users: (WWII) Argentina. Netherlands East Indies. Turkey.