Boeing B-17 Flying Fortress

B-17 Flying Fortress
B17 - Chino Airshow 2014 (framed).jpg
A B-17G performing at the 2014 Chino Airshow
RoleHeavy bomber
National originUnited States
First flight28 July 1935; 84 years ago (1935-07-28)[1]
IntroductionApril 1938; 81 years ago (1938-04)
Retired1968 (Brazilian Air Force)
Primary usersUnited States Army Air Forces
Royal Air Force
Number built12,731[2][3]
Unit cost
  • US$238,329 (1945)[4]
  • US$2.7 million (in 2018 dollars)[5]
Developed intoBoeing 307 Stratoliner

The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Competing against Douglas and Martin for a contract to build 200 bombers, the Boeing entry (prototype Model 299/XB-17) outperformed both competitors and exceeded the air corps' performance specifications. Although Boeing lost the contract (to the Douglas B-18 Bolo) because the prototype crashed, the air corps ordered 13 more B-17s for further evaluation. From its introduction in 1938, the B-17 Flying Fortress evolved through numerous design advances,[6][7] becoming the third-most produced bomber of all time, behind the four-engined B-24 and the multirole, twin-engined Ju 88.

The B-17 was primarily employed by the USAAF in the daylight strategic bombing campaign of World War II against German industrial and military targets. The United States Eighth Air Force, based at many airfields in central, eastern and southern England, and the Fifteenth Air Force, based in Italy, complemented the RAF Bomber Command's nighttime area bombing in the Combined Bomber Offensive to help secure air superiority over the cities, factories and battlefields of Western Europe in preparation for the invasion of France in 1944.[8] The B-17 also participated to a lesser extent in the War in the Pacific, early in World War II, where it conducted raids against Japanese shipping and airfields.[9]

From its prewar inception, the USAAC (by June 1941, the USAAF) promoted the aircraft as a strategic weapon; it was a relatively fast, high-flying, long-range bomber with heavy defensive armament at the expense of bombload. It developed a reputation for toughness based upon stories and photos of badly damaged B-17s safely returning to base. The B-17 dropped more bombs than any other U.S. aircraft in World War II. Of approximately 1.5 million tons of bombs dropped on Nazi Germany and its occupied territories by U.S. aircraft, over 640,000 tons were dropped from B-17s.[10] In addition to its role as a bomber, the B-17 was also employed as a transport, antisubmarine aircraft, drone controller, and search-and-rescue aircraft.

As of October 2019, 9 aircraft remain airworthy, though none of them were ever flown in combat. Dozens more are in storage or on static display. The oldest of these is a D-series flown in combat in the Pacific and the Caribbean.



Model 299 NX13372
Gun turret atop the Model 299's nose glazing
Crashed Model 299
Boeing Y1B-17 in flight

On 8 August 1934, the USAAC tendered a proposal for a multiengine bomber to replace the Martin B-10. The Air Corps was looking for a bomber capable of reinforcing the air forces in Hawaii, Panama, and Alaska.[11] Requirements were for it to carry a "useful bombload" at an altitude of 10,000 ft (3,000 m) for 10 hours with a top speed of at least 200 mph (320 km/h).[12]

They also desired, but did not require, a range of 2,000 mi (3,200 km) and a speed of 250 mph (400 km/h). The competition for the air corps contract was to be decided by a "fly-off" between Boeing's design, the Douglas DB-1, and the Martin Model 146 at Wilbur Wright Field in Dayton, Ohio.

The prototype B-17, with the Boeing factory designation of Model 299, was designed by a team of engineers led by E. Gifford Emery and Edward Curtis Wells, and was built at Boeing's own expense.[13] It combined features of the company's experimental XB-15 bomber and 247 transport.[12] The B-17's armament consisted of five .30 caliber (7.62 mm) machine guns, with a payload up to 4,800 lb (2,200 kg) of bombs on two racks in the bomb bay behind the cockpit. The aircraft was powered by four Pratt & Whitney R-1690 Hornet radial engines, each producing 750 hp (600 kW) at 7,000 ft (2,100 m).[14]

The first flight of the Model 299 was on 28 July 1935 with Boeing chief test pilot Leslie Tower at the controls.[1][15] The day before, Richard Williams, a reporter for The Seattle Times, coined the name "Flying Fortress" when – observing the large number of machine guns sticking out from the new airplane – he described it as a "15-ton flying fortress" in a picture caption.[16] The most distinct mount was in the nose, which allowed the single machine gun to be fired toward nearly all frontal angles.[17]

Boeing was quick to see the value of the name and had it trademarked for use.[note 1] Boeing also claimed in some of the early press releases that Model 299 was the first combat aircraft that could continue its mission if one of its four engines failed.[18] On 20 August 1935, the prototype flew from Seattle to Wright Field in nine hours and three minutes with an average cruising speed of 252 miles per hour (406 km/h), much faster than the competition.[19]

At the fly-off, the four-engined Boeing's performance was superior to those of the twin-engined DB-1 and Model 146. Major General Frank Maxwell Andrews of the GHQ Air Force believed that the capabilities of large four-engined aircraft exceeded those of shorter-ranged, twin-engined aircraft, and that the B-17 was better suited to new, emerging USAAC doctrine.[20] His opinions were shared by the air corps procurement officers, and even before the competition had finished, they suggested buying 65 B-17s.[21][22]

Development continued on the Boeing Model 299, and on 30 October 1935, Army Air Corps test pilot Major Ployer Peter Hill and Boeing employee Les Tower took the Model 299 on a second evaluation flight. The crew forgot to disengage the "gust locks", which locked control surfaces in place while the aircraft was parked on the ground, and after takeoff, the aircraft entered a steep climb, stalled, nosed over, and crashed, killing Hill and Tower (other observers survived with injuries).[23][24][note 2]

The crashed Model 299 could not finish the evaluation, disqualifying it from the competition.[22] While the air corps was still enthusiastic about the aircraft's potential, army officials were daunted by its cost;[25] Douglas quoted a unit price of $58,200 (equivalent to $1.06 million today) based on a production order of 220 aircraft, compared with $99,620 ($1.82 million today) from Boeing.[26] Army Chief of Staff Malin Craig cancelled the order for 65 YB-17s, and ordered 133 of the twin-engined Douglas B-18 Bolo, instead.[21][22]

The loss was not total... but Boeing's hopes for a substantial bomber contract were dashed.

— Peter Bowers, 1976[27]

Initial orders

B-17Bs at March Field, California, prior to attack on Pearl Harbor, with framed nose glazing of the style retained through the B-17E model
Nose of a B-17G being restored at the Mighty Eighth Air Force Museum

Regardless, the USAAC had been impressed by the prototype's performance, and on 17 January 1936, through a legal loophole,[28][29] the Air Corps ordered 13 YB-17s (designated Y1B-17 after November 1936 to denote its special F-1 funding) for service testing.[22] The YB-17 incorporated a number of significant changes from the Model 299, including more powerful Wright R-1820-39 Cyclone engines. Although the prototype was company-owned and never received a military serial (the B-17 designation itself did not appear officially until January 1936, nearly three months after the prototype crashed),[30] the term "XB-17" was retroactively applied to the NX13372's airframe and has entered the lexicon to describe the first Flying Fortress.

Between 1 March and 4 August 1937, 12 of the 13 Y1B-17s were delivered to the 2nd Bombardment Group at Langley Field in Virginia for operational development and flight tests.[31] One suggestion adopted was the use of a preflight checklist to avoid accidents such as that which befell the Model 299.[29][32][note 3] In one of their first missions, three B-17s, directed by lead navigator Lieutenant Curtis LeMay, were sent by General Andrews to "intercept" and photograph the Italian ocean liner Rex 610 miles (980 km) off the Atlantic coast.[34] The mission was successful and widely publicized.[35][36] The 13th Y1B-17 was delivered to the Material Division at Wright Field, Ohio, to be used for flight testing.[37]

A 14th Y1B-17 (37-369), originally constructed for ground testing of the airframe's strength, was upgraded and fitted with exhaust-driven General Electric turbochargers.[38] Scheduled to fly in 1937, it encountered problems with the turbochargers, and its first flight was delayed until 29 April 1938.[39] The aircraft was delivered to the army on 31 January 1939.[40] Once service testing was complete, the Y1B-17s and Y1B-17A were redesignated B-17 and B-17A, respectively, to signify the change to operational status.[41]

Opposition to the air corps' ambitions for the acquisition of more B-17s faded, and in late 1937, 10 more aircraft designated B-17B were ordered to equip two bombardment groups, one on each U.S. coast.[42] Improved with larger flaps and rudder and a well-framed, 10-panel plexiglas nose, the B-17Bs were delivered in five small batches between July 1939 and March 1940. In July 1940, an order for 512 B-17s was issued,[43] but at the time of the attack on Pearl Harbor, fewer than 200 were in service with the army.[29]

A total of 155 B-17s of all variants was delivered between 11 January 1937 and 30 November 1941, but production quickly accelerated, with the B-17 once holding the record for the highest production rate for any large aircraft.[44][note 4] The aircraft went on to serve in every World War II combat zone, and by the time production ended in May 1945, 12,731 aircraft had been built by Boeing, Douglas, and Vega (a subsidiary of Lockheed).[45][46][47][48]

Though the crash of the prototype 299 in 1935 had almost wiped out Boeing, now it was seen as a boon. Instead of building models based on experimental engineering, Boeing had been hard at work developing their bomber and now had versions ready for production far better than would have been possible otherwise. One of the most significant weapons of World War II would be ready, but only by a hair.

— Jeff Ethell, 1985[43]
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