In November 1932, politician Stanley Baldwin, who was essentially the de facto Prime Minister of Great Britain at the time, gave a speech warning of the potential horrors of a future war. In it he quite famously predicted that “The bomber will always get through”.
Baldwin believed that modern bomber aircraft then coming into service had the potential to destroy enemy populations and centres of production, slaughtering thousands – possibly hundred of thousands – in a frighteningly short time span.
As it turned out, and as the Second World War demonstrated, Baldwin was partially correct. By that point improved technologies in both detection, direction and in fighter aircraft made bombing a far more expensive process and civilian centres proved more resilient to attack than expected. Baldwin’s prediction didn’t ultimately come true until the development of the atomic bomb.
But in 1932, when Baldwin delivered his speech, the balance did very much appear to be in favour of the bomber. And if there was an aircraft that typified this, it was the American Martin B-10.
It seems odd to look at this rather lumpy appearing aircraft today and think that, in its day, it was a revolutionary design, introducing features that would become largely standard in bomber aircraft all over the world by the Second World War. Because the B-10’s combined for the first time an all-metal airframe, monoplane layout, enclosed crew positions and rotating gun turret’s. It also had retractable landing gear, an enclosed and spacious internal bomb bay and streamlined engine cowlings.
Other aircraft had up to that point used some of these, but the B-10 was the first to put them all into one design.
Development began in 1930 in response to a 1929 United States Army Air Corps requirement for a twin engine bomber. At the time, the USAAC had just bought into service the Keystone LB-series of bombers, which were little more than slightly improved First World War designs.
Martin’s initial proposals were rejected but believing that there would be a market for a modern bomber in the near future, the company proceeded with building a prototype at their own expense – the Martin 123. This took to the air in February 1932 and was handed over to the US military for testing in March, where it received the designation of XB-907.
The new aircraft was an intermediate design, featuring open positions for the pilot and nose-and-rear gunners, as well as less-efficient Townend cowlings on its two Wright radial engines that produced 600hp each. But despite this, the XB-907 demonstrated exceptional performance, achieving a top speed of 186mph (300km/h).
This almost matched the top speed of the Army Air Corps best fighter of the time, the Curtiss P-6E, and the Army Air Corps recognized that more was achievable. They requested some changes be made to the prototype, which Martin was happy to do.
These led to initially the XB-907A, which fitted more powerful engines and NACA cowlings, as well as a powered front gun turret, and ultimately to the XB-10, which featured fully enclosed positions for the crew, as well as more powerful engines.
These modifications, all carried out in a remarkably fast four months, meant that the XB-10 demonstrated a top speed of 207 mph (333 km/h). And this did outpace every fighter in service at the time, if only for a short period.
The remarkable aircraft won Martin the Collier Trophy for the most outstanding achievement in American aviation, and in January 1933 they received the first orders for forty-eight aircraft for the Army Air Corps. These aircraft were designated by Martin as the “139” and represented a mixed bag of different models equipped with different engines.
The first fourteen were YB-10s which had Wright R-1820-25 engines which produced 675hp, followed by a single YB-10A that had turbocharging.
These were followed by seven YB-12s with a pair of 775 hp Pratt-Whitney R-1690-11 Hornet engines and twenty-five B-12As which were similar to the YB-12, but with increased fuel capacity and some of which were tested with floats.
The final aircraft of this order was the single YB-14. This was fitted experimentally with Twin Wasp engines that produced 950hp, but despite the improved performance was converted back to B-12 configuration after testing.
After assessing the various configurations, the Air Corps settled in 1934 on what was designated as the B-10B and ordered 103 of this type.
The B-10B was fitted with Wright R-1820-33 Cyclone 9-cylinder radial engines that produced 775hp. These gave the aircraft a top speed of 213 mph (343km/h) and a maximum range of 1,240 miles (2,000km).
Generally carrying a three-man crew, though four was possible, the B-10B had an armament of three .30-calibre Browning machine guns in nose turret and in the dorsal and ventral positions and could carry a bombload of up to 2,260 lbs (1,030 kgs).
Deliveries commenced in 1935 and were completed in 1936, and the YB-10s, B-10Bs and B-12s were the prime striking component of the Air Corps. They served throughout the United States, as well as in Panama and the Philippines, and were basically a quantum leap on the old-fashioned biplanes still operated by some of the USAAC’s bomber squadrons.
In fact, General Henry H. Arnold, who would command the USAAF during World War Two and performed record breaking flights in the B-10B, described the aircraft as “the airpower wonder of its day”.
Despite this, the USAAC had already seen the rapid pace that aero technology was going in and were making plans for bigger and more powerful aircraft, plans that led ultimately to the B-17 Flying Fortress. This would lead to the B-10 having a short frontline life in US service, and they were rapidly replaced by later aircraft. By 1940 they were serving as target towers and in US-based reconnaissance squadrons
But this was in the future and with their Air Corps contract fulfilled in 1936, Martin was allowed to look for export orders. Of which, unsurprisingly, there were plenty.
After all, though the B-10 was rapidly falling by the wayside as other companies produced bombers surpassing its performance it was still vastly better than many of the aircraft being flown by minor air forces. And as a result, Martin saw a lot of international customers purchase their export version -the Martin 139 – which in turn led to a lot of combat service, much of it little remembered.
Of the purchasers whose Martin 139s didn’t see any combat, the Argentines, one of whose aircraft is seen below, bought 35; the Soviet Union bought a single aircraft for testing; and Turkey purchased twenty.
There were also talks to license build the 139 in Spain, but the outbreak of the Spanish Civil War ended that before it could be agreed.
The first B-10s to see combat were those sold to the Republic of China. These were delivered in 1937, just in time to get thrown into the conflagration of the Second Sino-Japanese War.
Although only a total of nine B-10s, designated as Martin 139WCs, were ultimately used by the Chinese, they saw heavy use attacking Japanese positions and achieved at least one remarkable first.
On 20 May 1938, two Chinese B-10s conducted an audacious raid on Japan itself. Early in morning, the aircraft penetrated the defence of the home island and overflew the city of Nagasaki, where they discharged their payload -two million leaflets.
The Chinese recognized that two bombers weren’t going to do any worthwhile damage to Japanese industry, and therefore thought it better to use the flight to try to show to the Japanese public the atrocities being conducted in China by their military. It was ultimately for naught but that doesn’t detract from the fact that it was a remarkable mission.
By far the biggest sale – and second biggest user of the type after the USAAC – was to the Dutch East Indies. In 1935 the Dutch colonial authorities decided that modern bombers were a perfect answer for defending their far flung and distant colony, and so very quickly began to make assessments of the B-10.
Initially they examined licence production, but that proved something the Dutch aero industry of the time was not able to do in any numbers because of the B-10s advanced all-metal structure. So, they made gradually increasing orders, receiving thirteen Martin 139WH-1 in 1937 and twenty-six improved -WH-2s in 1938.
This was followed by a final order for what was the ultimate variants of the B-10, forty WH-3s and 42 WH-3As, also known as the Martin 166.
These had improved aerodynamics, a solid glazed “greenhouse” that linked the cockpit to the rear position and more powerful engines, with the WH-3A having two Wright Cyclone G-105’s that each produced 1,000hp. They also featured external bomb shackles that could double payload over short distances.
In total, the Dutch East Indies ordered 121 Martins for use. Though some were lost in accidents, at the time of the Japanese invasion of Indonesia in December 1941 around one hundred of the aircraft were available for use in combat and training squadrons. These saw continuous use attacking the initial landings, and then raiding Japanese forces as they campaigned across the archipelago.
But the Martin, the wonder weapon of 1932, was very much out-of-date a decade later in the face of modern Japanese fighters, as well as suffering heavy losses from attacks on their airfields. To be fair, newer bombers were proving just as susceptible, and the Martin’s battled on until early March when, with surrender looming the few survivors left in Dutch hands retreated to Australia.
The final user was the Kingdom of Siam (now known as Thailand). That country initially bought six Martin’s, company designated as the 139WSM, in 1937. These would subsequently see action in the Franco-Thai War of late 1940 -early ’41, bombing airfields and towns in French Indo-China.
When Thailand fell fully under Japanese control, the Royal Thai Air Force was supplied with nine aircraft captured from the Dutch in the East Indies.
The war proved little kinder to the Martin’s in the RTAF than in others, but five survived the war. These proved to be the final B-10s to remain in service, with the Royal Thai Air Force finally retiring them in 1949.
Despite their revolutionary nature when first constructed, the Martin B-10 suffered the fate of so many such aircraft, rapidly finding itself outclassed by new machines inspired by what it had demonstrated as possible.
Today only one of the 348 built still survives. This, originally one of the Argentine B-10s, now dwells at the Air Force Museum in Dayton, Ohio, painted to replicate one of the B-10s used in General Arnold’s record-breaking flights.
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