B-17 Flying Fortress Totally Explained

Everything about Boeing B-17 Flying Fortress totally explained

The Boeing B-17 Flying Fortress is a four-engine heavy bomber aircraft developed for the U.S. Army Air Corps (USAAC). Competing against Douglas and Martin for a contract to build 200 bombers, the Boeing entry outperformed both the other competitors and more than met the Air Corps' expectations. Although Boeing lost the contract due to the prototype's crash, the Air Corps was so impressed with Boeing's design that they ordered 13 B-17s. The B-17 Flying Fortress went on to enter full-scale production and was considered the first truly mass-produced large aircraft, eventually evolving through numerous design advancements, from B-17A to G.
The B-17 was primarily employed in the daylight precision strategic bombing campaign of World War II against German industrial, civilian and military targets. The United States Eighth Air Force based in England and the Fifteenth Air Force based in Italy complemented the RAF Bomber Command's nighttime area bombing in Operation Pointblank, to help secure air superiority over the cities, factories and battlefields of Western Europe in preparation for Operation Overlord. The B-17 also participated, to a lesser extent, in the War in the Pacific, where it conducted raids against Japanese shipping.
From its pre-war inception, the USAAC touted the aircraft as a strategic weapon; it was a potent, high-flying, long-ranging bomber capable of unleashing great destruction yet able to defend itself. With the ability to return home despite extensive battle damage, its durability, especially in belly-landings and ditchings, quickly took on mythic proportions. Stories and photos of B-17s surviving battle damage widely circulated, boosting its iconic status. Despite an inferior range and bombload compared to the more numerous B-24 Liberator, a survey of Eighth Air Force crews showed a much higher rate of satisfaction in the B-17. With a service ceiling greater than any of its Allied contemporaries, the B-17 established itself as a superb weapons system, dropping more bombs than any other U.S. aircraft in World War II. Of the 1.5 million tonnes of bombs dropped on Germany, 500,000 were dropped from B-17s.

Design and development

On 8 August 1934, the U.S. Army Air Corps (USAAC) tendered a proposal for a multi-engined bomber to replace the Martin B-10. Requirements were that it would carry a "useful bombload" at an altitude of 10,000 ft (3 km) for ten hours with a top speed of at least 200 mph (320 km/h). They also desired, but didn't require, a range of 2,000 miles (3200 km) and a speed of 250 mph (400 km/h). The Air Corps were looking for a bomber capable of reinforcing the air forces in Hawaii, Panama, and Alaska. The competition would be decided by a "fly-off" at Wright Field in Dayton, Ohio. Boeing competed with the Douglas DB-1 and Martin Model 146 for the Air Corps contract.
   The prototype B-17, designated Model 299, was designed by a team of engineers led by E. Gifford Emery and Edward Curtis Wells and built at Boeing's own expense. Boeing was quick to see the value of the name and had it trademarked for use. On 20 August, the prototype flew from Seattle to Wright Field in nine hours and three minutes at an average speed of 235 mph (378 km/h), much faster than the competition. Development continued on the Boeing Model 299, and on 30 October 1935, the Army Air Corps test-pilots Ployer, Hill, and Tower, took the Model 299 on a second evaluation flight. The crew forgot to disengage the airplane's "gust lock," a device that held the bomber's movable control surfaces in place while the plane was parked on the ground, and having taken off, the aircraft entered a steep climb, stalled, nosed over and crashed, killing two. The crashed Model 299 couldn't finish the evaluation, and while the Air Corps was still enthusiastic about the aircraft's potential, Army officials were daunted by the much greater expense per aircraft. Army Chief of Staff Malin Craig cancelled the order for 67 B-17s, and ordered 133 of the twin-engine Douglas B-18 Bolo instead. 13 YB-17s for service testing. The YB-17 incorporated a number of significant changes from the Model 299, including more powerful Wright R-1820-39 Cyclone engines replacing the original Pratt & Whitneys.
   On 1 March 1937, 12 of the 13 YB-17s were delivered to the 2nd Bombardment Group at Langley Field in Virginia, and used to help develop heavy bomber techniques and work out other bugs.
   The 13th YB-17 was delivered to the Material Division at Wright Field, Ohio, to be used for flight testing.
   A 14th YB-17 (37-369), originally constructed for ground testing of the airframe's strength, was upgraded and fitted with exhaust-driven turbochargers. Scheduled to fly in 1937, it encountered problems with the turbochargers and its first flight was delayed until 29 April 1938. Modifications cost Boeing US$100,000 and took until spring 1939 to complete, but resulted in an increased service ceiling and maximum speed. The aircraft was delivered to the Army on 31 January 1939 and was redesignated B-17A to signify the first operational variant.
   In late 1937, the Air Corps ordered ten more aircraft, designated B-17B and, soon after, another 29.
   Prior to the attack on Pearl Harbor, fewer than 200 B-17s were in service with the Army, 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).

Operational history

The B-17 began operations in World War II with the RAF in 1941, USAAF Eighth Air Force and Fifteenth Air Force units in 1942, and was primarily involved in the daylight precision strategic bombing campaign against German industrial targets. Operation Pointblank guided attacks in preparation for a ground assault.
During World War II, the B-17 equipped 32 overseas combat groups, inventory peaking in August 1944 at 4,574 USAAF aircraft worldwide, and dropped 640,036 long tons (650,195 tonnes) of bombs on European targets (compared to 452,508 tons (451,691 tonnes) dropped by the Liberator and 463,544 tons (420,520 tonnes) dropped by all other U.S. aircraft). Approximately 4,750, or one third, of B-17s built were lost in combat. At the time, the Air Corps considered high-altitude flight to be 20,000 ft (6 km) but, to avoid being intercepted by fighter aircraft, the RAF bombed the naval barracks from 30,000 ft (9 km). They were unable to hit their targets and temperatures were so low that the machine guns froze up. On 24 July, they tried another target, Brest in France, but again missed completely.
By September, after the RAF had lost eight B-17Cs in combat or to accidents, Bomber Command had abandoned daylight bombing raids due to the Fortress I's poor performance. The remaining aircraft were transferred to different commands for deployment to various duties including coastal defence. A Fortress from No. 206 Squadron RAF sank U-627 on 27 October 1942: the first of 11 U-boat kills credited to RAF Fortress bombers during the war.

The USAAF

The Air Corps (renamed United States Army Air Forces or USAAF in 1941), utilizing the B-17 and other bombers, bombed from high altitudes using the then-secret Norden Bombsight, which was an optical electro-mechanical gyro-stabilized computer. During daylight bombing missions and sorties, the device was able to determine, from variables input by the bombardier, the point in space at which the bomber's ordnance type should be released to hit the target. The bombardier essentially took over flight control of the aircraft during the bomb run, maintaining a level attitude during the final moments.
   The USAAF began building up its air forces in Europe using B-17Es soon after entering the war. The first Eighth Air Force units arrived in High Wycombe, England on 12 May 1942, to form the 97th Bomb Group. The attacks did succeed, however, in diverting about half the Luftwaffe's fighter force to anti-bomber operations.
   Since the airfield bombings were not appreciably reducing German fighter strength, additional B-17 groups were formed, Eaker ordered major missions deeper into Germany against important industrial targets. The 8th Air Force then targeted the ball-bearing factories in Schweinfurt, hoping to cripple the war effort there. The first raid on 17 August 1943 didn't result in critical damage to the factories, with the 230 attacking B-17s being intercepted by an estimated 300 Luftwaffe fighters. Thirty-six aircraft were shot down with the loss of 200 men, and coupled with a raid earlier in the day against Regensburg, a total of 60 B-17s were lost that day.
   A second attempt on 14 October 1943 would later come to be known as "Black Thursday". Of the 291 attacking Fortresses, 59 were shot down over Germany, one ditched in the English Channel, five crashed in England, and 12 more were scrapped due to battle damage or crash-landings (more by AA guns than the Luftwaffe), a total loss of 77 B-17s. One hundred and twenty-two bombers were damaged to some degree and needed repairs before their next flight. Out of 2,900 men in the crews, about 650 men didn't return, although some survived as POWs. Five were killed and 43 wounded in the damaged aircraft that made it home, and 594 were listed as Missing in Action. Only 33 bombers landed without damage. These losses of air crews couldn't be sustained, and the USAAF, recognizing the vulnerability of heavy bombers against interceptors, suspended daylight bomber raids deep into Germany until the development of an escort fighter that could protect the bombers all the way from the United Kingdom to Germany and back. The Eighth Air Force alone lost 176 bombers in October 1943. The Eighth Air Force was to suffer similar casualties on 11 January 1944 on missions to Oschersleben, Halberstadt and Brunswick. Doolittle had ordered the mission to be cancelled as the weather deteriorated, but the lead units had already entered hostile air space and continued with the mission. Most of the escorts turned back or missed the rendezvous, as a result 60 B-17s were destroyed A third raid on Schweinfurt on 24 February 1944 highlighted what came to be known as "Big Week". With P-51 Mustang and P-47 Thunderbolt fighters (equipped with improved drop tanks to extend their range) escorting the American heavies all the way to and from the targets, only 11 of 231 B-17s were lost. The escort fighters reduced the loss rate to below seven percent, with only 247 B-17s lost in 3500 sorties while taking part in the Big Week raids.
   By September 1944, 27 of the 40 bomb groups of the Eighth Air Force and six of the 21 groups of the Fifteenth Air Force utilized B-17s. Losses to flak continued to take a high toll of heavy bombers through 1944, but by 27 April 1945, (two days after the last heavy bombing mission in Europe) the rate of aircraft loss was so low that replacement aircraft were no longer arriving and the number of bombers per bomb group was reduced. The Combined Bomber Offensive was effectively complete.

Pacific Theater

Only five B-17 groups operated in the Southwest Pacific theater, and all converted to other types in 1943. On 7 December 1941, A group of B-17's were flown into Pearl Harbor from California for delivery and arrived during the Japanese attack. One of the surviving pilots, Leonard "Smitty" Smith Humiston reported that he thought the U.S. Navy was giving the flight a 21 gun salute to celebrate the arrival of the bombers, after which he realized that Pearl Harbor was under attack. He came under fire from Japanese fighter aircraft, suffering more than 200 bullet holes in his aircraft. His crew was unharmed with the exception of 1 crewman who suffered an abrasion on his hand. Enemy activity near his destination forced an abort to an adjacent pineapple field where he landed safely.
By 1941, the Far East Air Force (FEAF) based at Clark Field in the Philippines had 35 B-17s, with the War Department eventually planning to raise that to 165. When the FEAF received word of the attack on Pearl Harbor, General Lewis H. Brereton sent his bombers and fighters on various patrol missions to prevent them from being caught on the ground. Brereton planned B-17 raids on Japanese air fields in Formosa, in accordance with Rainbow 5 war plan directives, but this was overruled by General Douglas MacArthur. A series of disputed discussions and decisions, followed by several confusing and false reports of air attacks, delayed the authorization of the sortie. By the time that the B-17s and escorting Curtiss P-40 fighters were about to get airborne, they were destroyed by Japanese bombers of the 11th Air Fleet. The FEAF lost fully half its aircraft during the first strike, and was all but destroyed over the next few days.
   Another early World War II Pacific engagement on 10 December 1941 involved Colin Kelly who reportedly crashed his B-17 into the Japanese battleship Haruna, which was later acknowledged as a near bomb miss on the light cruiser Ashigara; nonetheless that deed made him a celebrated war hero. Kelly's B-17C 40-2045 crashed about six miles (10 km) from Clark Field after he held the burning Fortress steady long enough for the surviving crew to bail out. Kelly was posthumously awarded the Distinguished Service Cross. Noted Japanese ace Saburo Sakai is credited with this kill, and in the process, gained respect for the ability of the Fortress to absorb punishment.
   B-17s were used in early battles of the Pacific with little success, notably the Battle of Coral Sea and Battle of Midway. While there, the Fifth Air Force B-17s were tasked with disrupting the Japanese sea lanes. Air Corps doctrine dictated bombing runs from high altitude, but it was soon discovered that only one percent of their bombs hit targets. However, B-17s were operating at heights too great for most A6M Zero fighters to reach, and the B-17's heavy gun armament was easily more than a match for lightly protected Japanese planes.
   On March 2 1943, six B-17s of the 64th Squadron attacked a major Japanese troop convoy from 10,000 ft (3 km) during the early stages of the Battle of the Bismarck Sea, off New Guinea, using skip bombing to sink three merchant ships including the Kyokusei Maru. A B-17 was shot down by a New Britain-based A6M Zero, whose pilot then machine-gunned some of the B-17 crew members as they descended in parachutes and attacked others in the water after they landed. Later, 13 B-17s bombed the convoy from medium altitude, causing the ships to disperse and prolonging the journey. The convoy was subsequently all but destroyed by a combination of low level strafing runs by Royal Australian Air Force Beaufighters, and skip bombing by USAAF B-25 Mitchells at 100 ft (30 m), while B-17s claimed five hits from higher altitudes.
   A peak of 168 B-17 bombers were in theater in September 1942, with all groups converting to other types by mid-1943.

Bomber defense

Before the advent of long-range fighter escorts, B-17s had only their .50 in (12.7 mm) caliber M2 Browning machine guns to rely on for defense during the bombing runs over Europe. As the war intensified, Boeing used feedback from aircrews to improve each new variant with increased armament and armor. The number of defensive guns increased from four 0.50 (12.7 mm) inch machine guns and one 0.30 inch (7.62 mm) nose machine gun in the B-17C, to 13 0.50 inch (12.7 mm) machine guns in the B-17G. But because the bombers couldn't maneuver when attacked by fighters, and during their final bomb run they needed to be flown straight and level, individual aircraft struggled to fend off a direct attack.
   A 1943 survey by the Air Corps found that over half the bombers shot down by the Germans, had left the protection of the main formation. To address this problem, the United States developed the bomb-group formation, which evolved into the staggered combat box formation where all the B-17s could safely cover any others in their formation with their machine guns, making a formation of the bombers a dangerous target to engage by enemy fighters.), and it wasn't until the advent of effective long-range fighter escorts (particularly the P-51 Mustang)— resulting in the degradation of the Luftwaffe as an effective interceptor force between February and June 1944 — that the B-17 became strategically potent.
   The B-17 was noted for its ability to absorb battle damage, still reach its target and bring its crew home safely. Wally Hoffman, a B-17 pilot with the Eighth Air Force during World War II, said, "The plane can be cut and slashed almost to pieces by enemy fire and bring its crew home." Martin Caidin reported one instance in which a B-17 suffered a midair collision with a Focke-Wulf 190, losing an engine and suffering serious damage to both the starboard horizontal stabilizer and the vertical stabilizer, and being knocked out of formation by the impact. The airplane was reported as shot down by observers, but it survived and brought its crew home without injury. Its toughness more than compensated for its shorter range and lighter bomb load when compared to the Consolidated B-24 Liberator or the British Avro Lancaster heavy bombers. Stories abound of B-17s returning to base with tails having been destroyed, with only a single engine functioning or even with large portions of wings having been damaged by flak. This durability, together with the large operational numbers in the Eighth Air Force and the fame achieved by the "Memphis Belle", made the B-17 a significant bomber aircraft of the war.
   The B-17 design went through eight major changes over the course of its production, culminating in the B-17G, differing from its immediate predecessor by the addition of a chin turret with two .50 inch (12.7 mm) caliber M2 Browning machine guns under the nose. This eliminated the B-17's main defensive weakness in head-on attacks.

The Luftwaffe

After examining wrecked B-17s and B-24s, Luftwaffe officers discovered that at least 20 hits with 20 mm shells fired from the rear could bring them down. Pilots of average ability hit the bombers with only about two percent of the rounds they fired, so to obtain 20 hits, the average pilot had to aim one thousand 20 mm rounds at the bomber. Early versions of the Fw 190, one of the best German interceptor fighters, were equipped with two 20 mm cannons and carried only 500 rounds. The fighter's firing range, 400 meters, was also shorter than the B-17's 1,000 meters, and so was vulnerable while closing in through that distance. The German fighters found that when attacking from the front, where fewer defensive guns were pointed, it only took four or five hits to bring a bomber down. To address the Fw 190's shortcomings, the number of cannons fitted was doubled to four with a corresponding increase in the amount of ammunition carried, and in 1944, a further upgrade to 30 mm MK 108 cannons was made, which could bring a bomber down in just a few hits.
The adoption, as a "stand-off" style of offense, of the Werfer-Granate 21 (W.Gr.21) Dodel rocket mortar, with one tubular launcher mounted under each wing panel on the Luftwaffe's single engined fighters, and two under each wing panel on a few Bf 110 daylight Zerstörer aircraft, had the promise of being a major weapon, but due to the ballistic drop of the fired rocket, and the low numbers of fighters fitted with the Dodel weapons, the W.Gr 21 never had a major effect on the combat box fomations of Fortresses. Also, the attempts of the Luftwaffe to fit heavy-calibre Bordkanone-series 37, 50 and even 75mm cannon on twin engined aircraft such as the special Ju 88P fighters, and even on one model of the Me 410 Hornisse, as anti-bomber weapons didn't have much effect on the American strategic bomber offensive. The Me 262 had moderate success against the B-17 late in the war. Equipped with the R4M rocket, it could fire from outside the range of the bombers' .50 caliber defensive guns and bring an aircraft down with one hit.
During World War II, after crash-landing or being forced down, approximately 40 B-17s were captured and refurbished by the Luftwaffe with about a dozen put back into the air. Given German markings and codenamed "Dornier Do 200", the captured B-17s were used for clandestine spy and reconnaissance missions by the Luftwaffe — most often used by the Luftwaffe unit known as Kampfgeschwader 200. One of the B-17s of KG200, bearing Luftwaffe markings A3+FB, was interned by Spain when it landed at Valencia airport, 27 June 1944, and remained there for the rest of the war. Some B-17s kept their Allied markings and were used in attempts to infiltrate B-17 formations and report on their position and altitude. The practice was initially successful, but the Army Air Force combat aircrews quickly developed and established standard procedures to first warn off, and then fire upon any "stranger" trying to join a group's formation. Few surviving aircraft were found by the Allies following the war.

Postwar history

Following World War II, the B-17 was declared obsolete and the Army Air Force retired most of its fleet. Flight crews ferried the bombers back across the Atlantic to the United States, where the majority were sold for scrap and melted down. The USAF Strategic Air Command had B-17 Flying Fortresses (called F-9s: for Fotorecon, at first, later RB-17s) in service from 1946 through 1951. About a dozen B-17s are still operable of some 50 airframes known to survive. Many of these surviving examples are surplus or training aircraft, which stayed in the U.S. during World War II. However, there are a few exceptions.
Several B-17s along with other World War II bombers were converted into airliners. Other B-17s saw extended and valiant service as converted aerial tankers used for fighting forest fires in the western United States.

Variants/design stages

Variant	Produced	First flight
Model 299	1	28 July 1935
YB-17A	1	29 April 1938.
B-17D	42	3 February 1941
B-17E	512	5 September 1941
B-17F	3,405	30 May 1942
B-17F-BO	2,300
B-17F-DL	605
B-17F-VE	500
B-17G	8,680
B-17G-BO	4,035
B-17G-DL	2,395
B-17G-VE	2,250
Grand total	12,731

The B-17 went through several alterations in each of its design stages and variants. Of the 13 YB-17s ordered for service testing, 12 were used by the 2nd Bomb Group of Langley Field, Virginia to develop heavy bombing techniques, and the 13th was used for flight testing at the Material Division at Wright Field, Ohio. Many B-17Gs were converted for other missions such as cargo hauling, engine testing and reconnaissance. Initially designated SB-17G, a number of B-17Gs were also converted for search-and-rescue duties, later to be redesignated B-17H.
Two versions of the B-17 were flown under different designations. These were the XB-38 and the YB-40. The XB-38 was an engine test-bed for Allison V-1710 liquid-cooled engines, should the Wright engines normally used on the B-17 become unavailable. The YB-40 was a heavily armed modification of the standard B-17 used before the P-51 Mustang, an effective long-range fighter, became available to act as escort. Additional armament included a power turret in the radio room, a chin turret (which went on to become standard with the B-17G) and twin .50 caliber (12.7 mm) guns in the waist positions. The ammunition load was over 11,000 rounds, making the YB-40 well over 10,000 lb (4,500 kg) heavier than a fully loaded B-17F. Unfortunately, the YB-40s with their numerous heavy modifications had trouble keeping up with empty bombers, and so, together with the advent of the P-51 Mustang, the project was abandoned and finally phased out in July 1943.
Late in World War II, at least 25 B-17s were fitted with radio controls, loaded with 20,000 pounds (9,000 kg) of high-explosives, dubbed "BQ-7 Aphrodite missiles". "Attacks on the V-site bunkers were also initiated by the Americans using radio controlled bombers packed with . of Torpex and TNT. Called Aphrodite drones, operation 'CASTOR' was begun on June 23 1944, using the 388th Bombardment Group at Knettishall. An airfield in a sparsely populated area of Norfolk was chosen at RAF Fersfield. The drone was usually a B-17 Fortress with a B-34 Ventura being used to control the aircraft and crash it onto its target." "The first four drones were sent to Mimoyecques, Siracourt, Watten and Wizernes on August 4, causing little damage. On the 6th two more B-17s were crashed on the Watten site with little success. The project came to a sudden end with the unexplained mid-air explosion over the Blyth estuary of a Liberator, part of the US Navy's contribution as project Anvil, en route for Heligoland piloted by Lieutenant" Joseph P. Kennedy Jr., future U.S. president John F. Kennedy's eldest brother. Blast damage was caused over a radius of five miles (8 km). British authorities were anxious that no similar accidents should again occur. Because few (if any) BQ-7s hit their target, the Aphrodite project was scrapped in early 1945. During and after World War II, a number of weapons were tested and used operationally on B-17s. Some of these weapons included "razons" (radio-guided) glide bombs, and Ford-Republic JB-2 Loons, also nicknamed Thunderbugs — American reverse-engineered models of the German V-1 Buzz Bomb. A much-used travelling airborne shot of a V-1/JB-2 launch in World War II documentaries was filmed from a USAF A-26 of the Air Proving Grounds, Eglin Air Force Base, launched from Santa Rosa Island, Florida. In the late 1950s, the last B-17s in United States Air Force service were QB-17 drones and DB-17P drone controllers, plus a few polished VB-17 squadron "hacks" (a 1953 request by the Wright Air Development Center to redesignate the QB-17s to Q-7 was turned down by Air Research & Development Command). The last operational mission flown by a USAF Fortress was conducted on 6 August 1959, when DB-17P 44-83684 directed QB-17G 44-83717 out of Holloman Air Force Base as a target for a Falcon air-to-air missile fired from an F-101 Voodoo fighter. A retirement ceremony was held several days later at Holloman, after which 44-83684 was retired to the Military Aircraft Storage and Disposition Center (MASDC) at Davis-Monthan Air Force Base.

Operators

Europe, where its shorter range and smaller bombload relative to other aircraft available didn't hamper it as much as in the Pacific Theater. Peak USAAF inventory (in August 1944) was 4,574 worldwide.

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