The emergence and rapid development of American bomber aviation was one of the most remarkable advances in the history of manned flight. The United States entered World War II with a mere handful of outmoded bombers, yet by war’s end it had managed to build the most advanced and powerful bomber fleet in the world. But even more important, the United States demonstrated that in a global war victory is crucially dependent on superiority in both quantity and quality of heavy bombers. The U.S. economy enabled that country to create an entirely new component within their military organization, namely strategic aviation, which can be used to pursue not only military but political and economic objectives as well. Production of heavy bombers in the United States during the war peaked at as many as 50 aircraft per day! Even on their luckiest days, the Axis powers were unable to shoot down as many, while in the meantime thousands of tons of explosives continued to pummel their cities and industrial centers. By the end of the war, the U.S. strategic bomber fleet was several times the size of the heavy bomber fleets of all other countries combined.
«Martin» B-10 – the primary aircraft of the American bomber fleet in the prewar period. Compared to the best of European designs it had insufficient self defense armament, small bomb load and limited range.
The origins of such astonishing success were humble indeed. In 1934, the United States Army fielded the new twin-engine Martin B-10 bomber, which remained the mainstay of the American bomber fleet until the end of the 1930s. Only 151 aircraft in all versions - including B-10, B-12, B-14 and the prototypes - were built. Another 206 machines were exported, most to the Netherlands and in smaller numbers to some countries. The B-10 even fought in World War II with the Chinese Air Force. Although, the aircraft was faster than any other American aircraft, its overall performance was inferior to European designs, especially in bombload and range. The Americans were determined to alter this state of affairs.
In February 1934, the U.S. Army Air Corps issued to Boeing, Douglas and Martin a specification designated “XBLR” and later known as “Project A,” for a super-long-range bomber capable of carrying 900 kg of ordnance over a distance of 8000 km. Martin's proposals were rejected at the early stages of development: the four-engine Martin XBLR, designated “XB-16,” never got off the drawing board. The six-engine Martin XB-16-2, presented in 1935, was also turned down.
The design proposed by Boeing received a working designation of “Boeing Model 294.” In the summer of 1934 the company started to assemble the prototype XBLR-1 aircraft, later dubbed “XB-15.” With a wing span of 45 meters, it was the largest airplane ever built in the United States at that time. The prototype, powered by four Pratt & Whitney R-1830-11 Twin Wasp engines rated at 850 hp each, rose into the air in October 1937. Its enormous cost, however, coupled with poor flight performance due to insufficient engine power, prevented it from ever going into production. The XB-15 remained in service as a cargo plane and set several world records in the area of cargo transportation.
Giant «Boeing» XB-15. The company spent a fortune to build this monster and was on the verge of bankruptcy.
Another example of gigantomania: «Douglas» XB-19. «Curtiss» P-40 fighter, flying alongside, gives you a sense of the true size of that colossus.
Douglas presented an innovative plan for its own four-engine bomber. However, the Great Depression was far from over, and, with money available for only one prototype, the cash-strapped government selected the Boeing XB-15. Financial difficulties also compelled Douglas to delay presentation of its prototype - the XBLR-2, later dubbed “XB-19,” until June 1941. With a wingspan of 65 meters and a length of more than 40 meters, it was a mammoth of a plane, beside which the huge XB-15 looked a toy. The XB-19 prototype rose into the air for the first time on June 27, 1941. Its bomb bays could carry more than 16 metric tons of ordnance! However, neither the original Wright R-3350-5 Cyclone engines, nor the 2600 hp Allison V-3420-11 that later replaced them were powerful enough to ensure a decent flight performance. In addition, the sum spent on construction of this monster was so enormous that the Air Corps refused even to consider launching it into production. Sharing the same fate as its competitor, the airplane remained in the U.S. as a transport vehicle for domestic mail.
It was also in 1934 that following the XBLR specification, the Air Corps issued a much less ambitious specification for a heavy bomber capable of carrying twice as much bombload as the B-10 over twice the distance. The specification, designated “35-26,” was issued to the same companies - Boeing, Douglas and Martin – with the winner to receive a production order for 220 machines.
Martin chose the easiest and cheapest route by upgrading its existing B-10/B-12 bomber. On the basis of its existing export version, the B-10 Model 139, the company created a new Model 146, designated “B-10B,” and presented it to the Evaluation Commission at Wright Field in August 1935 alongside the two competing designs. However, performance gains were so small that the offer was rejected as having no potential.
Douglas based its DB-1 proposal on its commercial DC-2 aircraft, which later became one of the best known cargo planes and passenger airliners. The company made a bare minimum of changes to the DC-2 airframe, adding self-protection guns, a bomb bay and additional seats for the crew. Simplicity and reliability carried the day, and in January 1936, the company received a production order for the bomber, now bearing the designation “B-18.” Under the first production contract, it made 133 machines including the prototype. An order for an additional 177 aircraft followed in July 1937, and in 1938 another 40 were built. Thus, by the beginning of 1940, the Douglas B-18 Bolo had become the principal bomber in the U.S. army inventory. Even in 1942, when the B-18 ceded this role to the B-17 , the Bolo continued to remain in service. Many were converted to the B-18B patrol/anti-sub configuration. Later, the aircraft received new Wright R-2600-3 engines rated at 1600 hp and in this upgraded version became known as the B-22. However, this improvement was limited to existing aircraft and no new B-22s were ever produced. In 1938 the aircraft benefitted from much more substantial design changes: the engines remained the same as on the B-22 version, the fuselage was extended and narrowed, the wing and empennage area increased, and a tail machine gun added. Known as the “Douglas B-23,” this newly upgraded model flew for the first time on July 27, 1939, demonstrating much better performance than its predecessor. By the end of 1939, all aircraft on order by the Army had been turned out, and the B-23 Dragon began its service. However, even this improved version was still inferior to the best of European bombers, which were already fighting in WWII. There were no further orders of the Douglas B-23 and the limited number that had been produced were converted to support aircraft.
Somewhat earlier, in the spring of 1937, the North American firm offered to modernize the Bolo for the Air Corps. The aircraft was outfitted with new Pratt & Whitney R-2180-1 Hornet engines rated at 1200 hp, a modification that almost doubled its bomb load. The prototype - Model NA-21, later designated “XB-21” - was approved, and in the summer of 1937, the Air Corps presented the company with a contract to build five pre-production YB-21s. However, work on this order came to a stop after only machine had been produced and for the same reason: the design could not measure up to those of the competition.
To Boeing the 35-26 turned out to be a decisive order. The failure of its B-9 bomber, the near failure of the 1933 Boeing model 247 airliner, and the huge cash outlays for the XB-15 had placed the company in a very difficult financial position. The future of Boeing or, to be more precise, its very existence hinged on receipt of a new production order. On September 26, 1934, the company's board of directors provided $275 thousand for the development of a prototype bomber to the 35-26 specifications; however, expenditures on the project actually came to double that amount.
«Douglas» B-18 «Bolo» - the primary American bomber at the beginning of 1940. Photo of a modern museum piece.
«Douglas» B-23 «Dragon» - the aircraft that was to replace «Bolo» as the primary U.S. bomber. It was much better than its predecessor, but due to a variety of reasons failed to fill that role.
The XB-21 prototype - one of the failed attempts to make a competitive bomber out of B-18 undertaken by North-American.
Experimental «Boeing» model 299 – future «Flying Fortress» and the last-ditch attempt of Boeing to remain afloat.
Led by Gifford Emery and Edward Wells, a Boeing design team set to work on a bomber designated “Model 299.” The experience with Model 247 and Model 294 aircraft had not been wasted. Actually, the future bomber was being developed on the basis of Boeing's 247 airliner, but powered by four engines instead of two. On July 17, 1935, the Model 299 prototype left Boeing's assembly plant in Seattle, and on July 28 it made its maiden flight. In the next three weeks it made another seven test flights, and on August 20, was brought to the Wright Field test range for comparative testing against the Martin Model 146 (M-10B) and the Douglas DB-1(B-18 Bolo) bombers. The results were quite impressive - even Boeing's designers seemed to be surprised at the aircraft’s outstanding performance. The aircraft not only exceeded by a large margin all design specifications but also easily outperformed all competitors. Witnessing this triumph, a reporter for the Seattle Times jokingly called the aircraft a “Flying Fortress” – and the name stuck.
On October 30, however, a tragedy befell the project – because of a pilot error the aircraft went out of control, crashed and was completely destroyed in the ensuing conflagration. Boeing's test pilot Tower perished in the crash. This accident could have meant disaster for Boeing, especially since the company had lost the competition and was on the verge of bankruptcy. The Douglas DB-1 was proclaimed winner, and Boeing lost a contract for 65 production aircraft. Fortunately, on January 12, 1936, the Air Corps presented Boeing with a consolation prize - an order for 13 pre-production aircraft. The new Y1B-17 bomber, however, had a number of design flaws related to its engine and landing gear which led to yet another crash on December 7, 1936. Boeing lost one more production contract as the U.S. Congress voted to purchase another 253 B-18s. The main reason behind this decision, however, was the precipitous cost of the new Boeing bomber - twice that of the Douglas Bolo. Nonetheless, the performance of the Y1B-17 so impressed the Air Corps Staff that they insisted on starting up production. The 13th and last aircraft of the pre-production run was powered by higher-rated R-1820-51 engines equipped with turbocompressors, which increased its maximum speed by 20%. The aircraft, designated “Y1B-17A,” made its first flight on April 29, 1938. In July 1939, this aircraft, after some alterations to its nose, went into production under the designation “B-17B.” In all, 39 bombers were made. To their consternation, Boeing executives soon discovered that production of the B-17B was generating losses instead of profits. Boeing demanded that the government agree to an increase in the bomber's purchasing price, threatening to terminate production in response to a refusal. Congress yielded and the next production run turned out the bomber at the new record price of $202500 per aircraft. 38 B-17C bombers were delivered to the U.S. Air Corps by the end of the autumn of 1940 and another 20, designated “Fortress I,” were supplied to Britain under the lend-lease agreement. Some time later, these 20 were sent back for upgrading to the B-17D configuration. This version appeared in production in 1941, and a total of 42 B-17D bombers were made. There was not much difference between the B, C and D versions. These aircraft constituted all the Fortresses with which the United States entered the war. Most of them were destroyed on the very first day of the war for the Americans without having participated in a single bombing mission. On December 7, 1941, all twelve B-17D bombers, stationed at Hickam Air Base in Pearl Harbor were destroyed by fire, while another 18 B-17Cs and B-17Ds were destroyed on the ground at the Clark Airfield in the Philippines. The only purported coup scored by this aircraft was when Captain Colin Kelly allegedly attacked the Japanese battleship Haruna: it was said that he intentionally flew his bomber into the enemy ship. In reality, the pilot perished in an attempt to control the bomber so that the rest of the crew could bail out. It was just a coincidence that the crash took place precisely when a Japanese ship (not the Haruna but a heavy cruiser) turned back toward its home base for needed repairs.
Some of the handful of B-17Bs.
B-17C «Fortress I» of the British Royal Air Force
B-17D, destroyed on December 7, 1941 at Hickam Air Base in Pearl Harbor.
