| B-17 Flying Fortress | |
|---|---|
| Boeing B-17E | |
| Role | Heavy bomber Strategic bomber |
| National origin | United States |
| Manufacturer | Boeing |
| First flight | 28 July 1935[1] |
| Introduction | April 1938 |
| Retired | 1968 (Brazilian Air Force) |
| Primary users | United States Army Air Forces Royal Air Force |
| Produced | 1936–1945 |
| Number built | 12,731[2] |
| Unit cost | US$238,329[3] |
| Variants | XB-38 Flying Fortress YB-40 Flying Fortress C-108 Flying Fortress |
| Developed into | Boeing 307 |
The Boeing B-17 Flying Fortress is a four-engine heavy bomber aircraft developed in the 1930s for the then-United States Army Air Corps (USAAC). Competing against Douglas and Martin for a contract to build 200 bombers, the Boeing entry outperformed both competitors and more than met the Air Corps' expectations. Although Boeing lost the contract because the prototype crashed, the Air Corps was so impressed with Boeing's design that they ordered 13 more B-17s for further evaluation. From its introduction in 1938, the B-17 Flying Fortress evolved through numerous design advances.
The B-17 was primarily employed by the United States Army Air Forces (USAAF) in the daylight precision strategic bombing campaign of World War II against German industrial and military targets. The United States Eighth Air Force based at Thorpe Abbotts airfield 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.[4] The B-17 also participated to a lesser extent in the War in the Pacific where it conducted raids against Japanese shipping and airfields.
From its pre-war inception, the USAAC (later USAAF) touted the aircraft as a strategic weapon; it was a potent, high-flying, long-range bomber that was able to defend itself, and to return home despite extensive battle damage. It quickly took on mythic proportions,[5][N 1][6] and widely circulated stories and photos of B-17s surviving battle damage increased its iconic status.[7] With a service ceiling greater than any of its Allied contemporaries, the B-17 established itself as an effective weapons system, dropping more bombs than any other U.S. aircraft in World War II. Of the 1.5 million metric tons of bombs dropped on Germany by U.S. aircraft, 640,000 tons were dropped from B-17s.[8]
As of September 2011, 13 airframes remain airworthy, with dozens more in storage or on static display.
Contents |
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. The Air Corps was looking for a bomber capable of reinforcing the air forces in Hawaii, Panama, and Alaska.[9] Requirements were that it would carry a "useful bombload" at an altitude of 10,000 feet (3 km) for 10 hours with a top speed of at least 200 miles per hour (320 km/h).[10]
They also desired, but did not require, a range of 2,000 miles (3,200 km) and a speed of 250 miles per hour (400 km/h). The competition for the Air Corps contract would be decided by a "fly-off" between Boeing's design, the Douglas DB-1 and the Martin Model 146 at Wright Field in Dayton, Ohio.
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.[11] It combined features of the experimental Boeing XB-15 bomber with the Boeing 247 transport airplane.[10] The B-17's armament consisted of up to 4,800 pounds (2,200 kg) of bombs on two racks in the bomb bay behind the cockpit, and five 0.30 inches (7.62 mm) machine guns, and it was powered by four Pratt & Whitney R-1690 "Hornet" radial engines each producing 750 horsepower (600 kW) at 7,000 feet (2,100 m).[12]
The first flight of the Model 299 was on 28 July 1935, with Boeing chief test-pilot Leslie Tower at the controls.[1][13] Richard Williams, a reporter for the Seattle Times coined the name "Flying Fortress" when the Model 299 was rolled out, bristling with multiple machine gun installations.[14] The most unique being the nose installation (see note for description and drawing) which allowed the single machine gun to be fired from about any frontal angle any approaching enemy fighter would take to attack the B-17 [15]
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 for what ever reason failed.[16] Boeing was quick to see the value of the name and had it trademarked for use. On 20 August 1935, the prototype flew from Seattle to Wright Field in nine hours and three minutes at an average cruising speed of 252 miles per hour (406 km/h), much faster than the competition.[17]
At the fly-off, the four-engine Boeing's performance was superior to those of the twin-engine DB-1 and Model 146. Then-Major General Frank Maxwell Andrews of the GHQ Air Force believed that the long-range capabilities of four-engine large aircraft were more efficient than shorter-ranged twin-engined airplanes, and that the B-17 was better suited to their doctrine.[18] His opinions were shared by the Air Corps procurement officers, and even before the competition had finished they suggested buying 65 B-17s.[19][20]
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; however, the crew forgot to disengage the airplane's "gust lock," a device that held the bomber's movable control surfaces in place while the aircraft was parked on the ground. Having taken off, the aircraft entered a steep climb, stalled, nosed over and crashed, killing Hill and Tower (other observers survived with injuries).[21][22][N 2]
The crashed Model 299 could not 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[23] (Douglas quoted a unit price of $58,200 based on a production order of 220 aircraft, compared with a price of $99,620 from Boeing[24]), and as the competition could not be completed Boeing was legally disqualified from the consideration for the contract.[20] Army Chief of Staff Malin Craig cancelled the order for 65 YB-17s, and ordered 133 of the twin-engine Douglas B-18 Bolo instead.[19][20]
Regardless, the USAAC had been impressed by the prototype's performance, and on 17 January 1936, through a legal loophole,[25] the Air Corps ordered 13 YB-17s (designated Y1B-17 after November 1936 to denote its special F-1 funding) for service testing.[20] 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. 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),[26] the term "XB-17" was retroactively applied to the 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.[27] One suggestion adopted was the use of a pre-flight checklist to avoid accidents such as that which befell the Model 299.[25][28][N 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.[29] The mission was successful and widely publicized.[30][31] The 13th Y1B-17 was delivered to the Material Division at Wright Field, Ohio, to be used for flight testing.[32]
A 14th Y1B-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.[33] The aircraft was delivered to the Army on 31 January 1939.[34] 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.[35]
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.[36] Improved with larger flaps, rudder and Plexiglas nose, the B-17Bs were delivered in five small batches between July 1939 and March 1940. In July 1940, a significant order for 512 B-17s was issued;[37] however, prior to the attack on Pearl Harbor, fewer than 200 B-17s were in service with the Army.[25]
A total of 155 B-17s of all variants were delivered between 11 January 1937 and 30 November 1941, but production quickly accelerated with the B-17 eventually setting the record for achieving the highest production rate for large aircraft.[38][N 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).[39]
| Variant | Produced | First flight |
|---|---|---|
| Model 299 | 1 | 28 July 1935[1] |
| YB-17 | 13 | 2 December 1936[40] |
| YB-17A | 1 | 29 April 1938.[33] |
| B-17B | 39 | 27 June 1939[41] |
| B-17C | 38 | 21 July 1940[42] |
| B-17D | 42 | 3 February 1941[43] |
| B-17E | 512 | 5 September 1941[44] |
| B-17F | 3,405 | 30 May 1942[45][46] |
| B-17F-BO | 2,300 | [45] |
| B-17F-DL | 605 | [45] |
| B-17F-VE | 500 | [45] |
| B-17G | 8,680 | |
| B-17G-BO | 4,035 | |
| B-17G-DL | 2,395 | |
| B-17G-VE | 2,250 | |
| Grand total | 11,931 |
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.[32] Experiments on this aircraft led to the use of a turbo-supercharger which would become standard on the B-17 line. A 14th aircraft, the YB-17A, originally destined for ground testing only and upgraded with the turbocharger,[47] was re-designated B-17A after testing had finished.[34][35]
As the production line developed, Boeing engineers continued to improve upon the basic design. To enhance performance at slower speeds, the B-17B was altered to include larger rudder and flaps.[41] The B-17C changed from gun blisters to flush, oval-shaped windows.[42] Models A through D of the B-17 were designed defensively, while the B-17E was the first model primarily focused on offensive warfare.[47]
The B-17E was an extensive revision of the design; the fuselage was extended by 10 ft (3.0 m), a much larger vertical fin and rudder were incorporated into the original design, and a gunner's position in the tail as well as an improved nose were added, resulting in a 20% increase in aircraft weight.[47] The engines were upgraded to more powerful versions multiple times throughout its production, and similarly, the gun stations were altered on numerous occasions to enhance their effectiveness.[48]
By the time the definitive B-17G appeared, the number of guns had been increased from seven to 13, the designs of the gun stations were finalized, and other adjustments were complete. The B-17G was the final version of the B-17, incorporating all changes made to its predecessor, the B-17F,[47] and in total 8,680 were built,[49] the last one (by Lockheed) on July 28 1945.[50] Many B-17Gs were converted for other missions such as cargo hauling, engine testing and reconnaissance.[51] Initially designated SB-17G, a number of B-17Gs were also converted for search-and-rescue duties, later to be redesignated B-17H.[52]
Two versions of the B-17 were flown under different designations, the XB-38 Flying Fortress and the YB-40 Flying Fortress. 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 only prototype XB-38 to fly crashed on its ninth flight and the type was abandoned, the V-1710 being kept for fighters.[53][54]
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 an additional dorsal turret in the radio room, a chin turret (which became standard with the B-17G) and twin .50 in (13 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. The YB-40s with their numerous heavy modifications had trouble keeping up with the lighter bombers once they had dropped their bombs, and so the project was abandoned and finally phased out in July 1943.[55][56][57]
Late in World War II, at least 25 B-17s were fitted with radio controls and television cameras, loaded with 20,000 lb (9,100 kg) of high-explosives and dubbed BQ-7 "Aphrodite missiles" for Operation Aphrodite. The operation, which involved remotely flying Aphrodite drones onto their targets by accompanying CQ-17 "mothership" control aircraft, was approved on June 26, 1944, and assigned the 388th Bombardment Group stationed at RAF Fersfield, a satellite of RAF Knettishall.[58]
The first four drones were sent to Mimoyecques, the Siracourt V-1 bunker, Watten and Wizernes on August 4, causing little damage. The project came to a sudden end with the unexplained mid-air explosion over the Blyth estuary of a B-24 Liberator, part of the United States 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 elder brother. Blast damage was caused over a radius of 5 miles (8.0 km). British authorities were anxious that no similar accidents should again occur, and the Aphrodite project was scrapped in early 1945.[58]
The B-17 began operations in World War II with the RAF in 1941 (but was not successful), and in the Southwest Pacific with the US Army. The 19th Bombardment Group had deployed to Clark Field in the Philippines a few weeks before the Japanese attack on Pearl Harbor as the first of a planned heavy bomber buildup in the Pacific. Half of the group's airplanes were wiped out on December 8, 1941 when they were caught on the ground during refueling and rearming for a planned attack on Japanese airfields on Formosa. The small force of B-17s operated against the Japanese invasion force until they were withdrawn to Darwin. In early 1942 the 7th Bombardment Group began arriving in Java with a mixed force of B-17s and LB-30/B-24s.[59] After the defeat in Java, the 19th withdrew to Australia where it continued in combat until it was sent back home by Gen. George C. Kenney when he arrived in Australia in mid-1942.[60] In July 1942 the first B-17s were sent to England to join Eighth Air Force. Later that year two groups moved to Algeria to join Twelfth Air Force for operations in North Africa. The B-17s were primarily involved in the daylight precision strategic bombing campaign against German targets ranging from U-boat pens, docks, warehouses and airfields to industrial targets such as aircraft factories.[61] In the campaign against German aircraft forces in preparation for the invasion of France, B-17 (and B-24 Liberator) raids were directed against German aircraft production while their presence drew the Luftwaffe fighters into battle with Allied fighters.[4]
Early models proved to be unsuitable for combat use over Europe and it was the B-17E that was first successfully used by the USAAF. The defense expected from bombers operating in close formation alone did not prove effective and the bombers needed fighter escorts to operate successfully.
During World War II, the B-17 equipped 32 overseas combat groups, inventory peaking in August 1944 at 4,574 USAAF aircraft worldwide.[62] B-17s dropped 640,036 short tons (580,631 metric tons) of bombs on European targets (compared to 452,508 short tons (410,508 metric tons) dropped by the Liberator and 463,544 short tons (420,520 metric tons) dropped by all other U.S. aircraft). The British heavy bombers, the Avro Lancaster and Handley Page Halifax, dropped 608,612 and 224,207[63] long tons respectively.
The Royal Air Force entered World War II with no heavy bomber of its own in service; the biggest available were long-range medium bombers such as the Vickers Wellington which could carry up to 4,500 lb of bombs.[64] While the Short Stirling and Handley Page Halifax would become its primary bombers by 1941, in early 1940 the RAF entered into an agreement with the U.S. Army Air Corps to be provided with 20 B-17Cs, which were given the service name Fortress I. Their first operation, against Wilhelmshaven on 8 July 1941 was unsuccessful;[65][66] on 24 July, the target was Brest, France, but again the bombers missed completely.
By September, after the RAF had lost eight B-17Cs in combat or to accidents and many instances of aborts due to mechanical problems, Bomber Command abandoned daylight bombing raids because of the Fortress I's poor performance. The experience showed both the RAF and USAAF that the B-17C was not ready for combat, and that improved defenses, larger bomb loads and more accurate bombing methods were required. However the USAAF continued using the B-17 as a "day" bomber, despite pleas from the RAF that attempted daylight bombing would be ineffective.[67]
As usage by Bomber Command had been curtailed, the RAF transferred its remaining Fortress I aircraft to Coastal Command for use as a long-range maritime patrol aircraft instead.[68] These were later augmented in August 1942 by 19 Fortress Mk II (B-17F) and 45 Fortress Mk IIA (B-17E). 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.[69] No. 223 Squadron, as part of 100 Group operated a small number of Fortresses in support of the bombing offensive for jamming German radar.[70]
The Air Corps (renamed United States Army Air Forces (USAAF) on June 20, 1941), using the B-17 and other bombers, bombed from high altitudes using the then-secret Norden bombsight, known as the "Blue Ox",[71][72] which was an optical electro-mechanical gyro-stabilized analog computer.[73] The device was able to determine, from variables input by the bombardier, the point at which the aircraft's bombs should be released to hit the target. The bombardier essentially took over flight control of the aircraft during the bomb run, maintaining a level altitude during the final moments before release.[74]
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.[75] On 17 August 1942, 12 B-17Es of the 97th, with the lead aircraft piloted by Major Paul Tibbets and carrying Brigadier General Ira Eaker as an observer, were escorted by RAF Spitfires on the first USAAF raid over Europe, against railroad marshalling yards at Rouen-Sotteville in France, while a further six aircraft flew a diversionary raid along the French coast.[76][77] The operation was a success, with only minor damage to two aircraft.
As the raids of the American bombing campaign grew in numbers and frequency, German interception efforts arose to respond to the bombers (such as during the attempted bombing of Kiel on 13 June 1943[78]) to the level where unescorted bombing missions became discouraged.[79]
The two different strategies of the American and British bomber commands were organized at the Casablanca Conference in January 1943. The resulting "Combined Bomber Offensive" would weaken the Wehrmacht, destroy German morale and establish air superiority through Operation Pointblank's destruction of German fighter strength in preparation of a ground offensive.[4] The USAAF bombers would attack by day, with British operations – chiefly against industrial cities – by night.
Operation Pointblank opened with attacks on targets in Western Europe. General Ira C. Eaker and the Eighth Air Force placed highest priority on attacks on the German aircraft industry, especially fighter assembly plants, engine factories and ball-bearing manufacturers.[4] Attacks began in April 1943 on heavily fortified key industrial plants in Bremen and Recklinghausen.[80]
Since the airfield bombings were not appreciably reducing German fighter strength, additional B-17 groups were formed, and 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 did not result in critical damage to the factories, with the 230 attacking B-17s being intercepted by an estimated 300 Luftwaffe fighters. The Germans shot down 36 aircraft 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.[81]
A second attempt on Schweinfurt on 14 October 1943 would later come to be known as "Black Thursday".[82] While the attack was successful at disrupting the entire works, severely curtailing work there for the remainder of the war, it was at an extreme cost.[83] Of the 291 attacking Fortresses, 60 were shot down over Germany, five crashed on approach to Britain, and 12 more were scrapped due to damage – a total loss of 77 B-17s.[84] One hundred and twenty-two bombers were damaged and needed repairs before their next flight. Out of 2,900 men in the crews, about 650 men did not return, although some survived as prisoners of war. Only 33 bombers landed without damage. These losses were a result of concentrated attacks by over 300 German fighters.[85]
Such high losses of air crews could not be sustained, and the USAAF, recognizing the vulnerability of heavy bombers to interceptors when operating alone, 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. At the same time, the German night fighting ability noticeably improved to counter the nighttime strikes, challenging the conventional faith in the cover of darkness.[86] The Eighth Air Force alone lost 176 bombers in October 1943,[87] and was to suffer similar casualties on 11 January 1944 on missions to Oschersleben, Halberstadt and Brunswick. Lieutenant General James Doolittle, commander of the Eighth, had ordered the second Schweinfurt 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, and as a result 60 B-17s were destroyed.[88][89] A third raid on Schweinfurt on 24 February 1944 highlighted what came to be known as "Big Week",[90] during which the bombing missions were directed against German aircraft production.[86] German fighters would have to respond, and the North American P-51 Mustang and Republic P-47 Thunderbolt fighters (equipped with improved drop tanks to extend their range) accompanying the American heavies all the way to and from the targets would engage them.[91] The escort fighters reduced the loss rate to below seven percent, with only 247 B-17s lost in 3,500 sorties while taking part in the Big Week raids.[92]
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 used 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.[93]
On 7 December 1941, a group of 12 B-17s of the 38th (four B-17C) and 88th (eight B-17E) Reconnaissance Squadrons, en route to reinforce the Philippines, were flown into Pearl Harbor from Hamilton Field, California, arriving during the attack on Pearl Harbor. Leonard "Smitty" Smith Humiston, co-pilot on First Lieutenant Robert H. Richards' B-17C, AAF S/N 40-2049, 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. The Fortress came under fire from Japanese fighter aircraft, though the crew was unharmed with the exception of one member who suffered an abrasion on his hand. Enemy activity forced an abort from Hickam Field to Bellows Field, where the aircraft overran the runway and into a ditch where it was then strafed. Although initially deemed repairable, 40-2049 (11th BG / 38th RS) received more than 200 bullet holes and never flew again. Ten of the 12 Fortresses survived the attack.[95]
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.[96] 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.[97] 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 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 half its aircraft during the first strike,[98] 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 heavy cruiser Ashigara. Nonetheless, this deed made him a celebrated war hero. Kelly's B-17C AAF S/N 40-2045 (19th BG / 30th BS) crashed about 6 mi (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.[99] 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.[100]
B-17s were used in early battles of the Pacific with little success, notably the Battle of Coral Sea[101] and Battle of Midway.[102] 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.[103] 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 North American B-25 Mitchells at 100 ft (30 m), while B-17s claimed five hits from higher altitudes.[104]
A peak of 168 B-17 bombers were in the Pacific theater in September 1942, with all groups converting to other types by mid-1943. In mid-1942 Gen. Arnold decided that the B-17 was inadequate for the kind of operations required in the Pacific and made plans to replace all of the B-17s in the theater with B-24s as soon as they became available. Although the conversion was not complete until mid-1943, B-17 combat operations in the Pacific theater came to an end after a little over a year.[105] Surviving airplanes were reassigned to the 54th Troop Carrier Wing's special airdrop section, and were used to drop supplies to ground forces operating in close contact with the enemy. Special airdrop B-17s supported Australian commandos operating near the Japanese stronghold at Rabaul, which had been the primary B-17 target in 1942 and early 1943.[106]
Before the advent of long-range fighter escorts, B-17s had only their .50 in (12.7 mm) 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.[107] The number of defensive guns increased from four 0.50 in (12.7 mm) machine guns and one 0.30 in (7.62 mm) nose machine gun in the B-17C, to thirteen 0.50 in (12.7 mm) machine guns in the B-17G. But because the bombers could not 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.[108] 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.[109] Luftwaffe "jagdflieger" (fighter pilots) likened attacking a B-17 combat box formation to encountering a fliegendes stachelschwein, or "flying porcupine". However, the use of this rigid formation meant that individual aircraft could not engage in evasive maneuvers: they had to always fly in a straight line, which made them vulnerable to the German flak. Additionally, German fighter aircraft later used the tactic of high-speed strafing passes rather than engaging with individual aircraft to inflict damage with minimum risk.
As a result, the B-17s' loss rate was up to 25% on some early missions (60 of 291 B-17s were lost in combat on the second Raid on Schweinfurt[110]), and it was not until the advent of long-range fighter escorts (particularly the North American 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."[111] Martin Caidin reported one instance in which a B-17 suffered a mid-air collision with a Focke-Wulf Fw 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.[112] 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.[113] 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. Other factors such as combat effectiveness and political issues also contributed to the B-17's success.[114]
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 in (12.7 mm) caliber M2 Browning machine guns under the nose. This eliminated the B-17's main defensive weakness in head-on attacks.
After examining wrecked B-17s and B-24s, Luftwaffe officers discovered that on average it took around 20 hits with 20 mm (0.79 in) shells fired from the rear to bring them down.[84] 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 fire one thousand 20 mm (0.79 in) rounds at a bomber.[84] Early versions of the Fw 190, one of the best German interceptor fighters, were equipped with two 20 mm (0.79 in) MG FF cannons, which carried only 500 rounds, and later with the better Mauser MG 151/20 cannons, which had a longer effective range than the MG FF weapon. 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.[84] 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 Rheinmetall-Borsig's 30 mm (1.2 in) MK 108 cannons was made, which could bring a bomber down in just a few hits.[84]
The adoption of the Werfer-Granate 21 (Wfr. Gr. 21) rocket mortar by the Luftwaffe in mid-August 1943 promised the introduction of a major "stand-off" style of offensive weapon – one strut-mounted tubular launcher was fixed under each wing panel on the Luftwaffe's single-engined fighters, and two under each wing panel of a few twin-engined Bf 110 daylight Zerstörer aircraft.[84] However, due to the ballistic drop of the fired rocket (despite the usual mounting of the launcher at about 15° upward orientation), and the small number of fighters fitted with the weapons, the Wfr. Gr. 21 never had a major effect on the combat box formations of Fortresses.[84] Also, the attempts of the Luftwaffe to fit heavy-calibre Bordkanone-series 37, 50 and even 75 mm (2.95 in) cannon as anti-bomber weapons on twin-engined aircraft such as the special Ju 88P fighters, as well as one model of the Me 410 Hornisse, did not have much effect on the American strategic bomber offensive. The Me 262 had moderate success against the B-17 late in the war however. With its usual nose-mounted armament of four MK 108 cannons, and with some examples later equipped with the R4M rocket, launched from underwing racks, it could fire from outside the range of the bombers' .50 in (12.7 mm) defensive guns and bring an aircraft down with one hit.[116]
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, the captured B-17s were used to determine the plane's vulnerabilities and to train German interceptor pilots in tactics.[117] Others, with the cover designations Dornier Do 200 and Do 288, were used as long-range transports by the Kampfgeschwader 200 special duties unit, carrying out agent drops and supplying secret airstrips in the Middle East and North Africa. They were chosen for these missions as being more suitable for the role than available German aircraft and not in an attempt to deceive the Allies, being operated in full Luftwaffe markings.[118][119] One of the B-17s of KG200, bearing Luftwaffe markings A3+FB, was interned by Spain when it landed at Valencia airfield, 27 June 1944, and remained there for the rest of the war.[75] 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 Forces 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.[75]
The U.S. did not offer B-17s to the Soviet Union, however, at least 73 aircraft were acquired by the Soviet Air Force. These were aircraft that landed with mechanical trouble during the shuttle bombing raids over Germany, or had been damaged by a Luftwaffe raid in Poltava. The Soviets restored 23 to flying condition and concentrated them in the 890th bomber regiment of the 45th bomber division but they never saw combat. In 1946 the regiment was assigned to the Kazan factory to aid in the Soviet effort to reproduce the Boeing B-29 as the Tupolev Tu-4.[120]
Three B-17 Flying Fortress were captured by the Japanese in the Philippines and Netherlands East Indies. At Clark Field they recovered the turbosupercharger of a B-17 and other spare parts. Eventually an entire B-17D was put together from the collection of parts. Another B-17E was restored in the Netherlands East Indies, from the remains of almost 15 B-17s found on airfields. The third B-17E was found in reasonable condition in the same area, after it crash landed at Djokjakarta, Java and was abandoned.
They were tested by the IJAAF Koku Gijutsu Kenkyujo (Air Technical Research Laboratory) at Tachikawa. In the spring of 1945 an American aerial photo of the Japanese Tachikawa air base revealed a large unknown Japanese four-engine bomber. After the war investigators discovered the aircraft was actually a B-17E.
Following the end of World War II, the B-17 was quickly phased out of use as a bomber and the Army Air Forces 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, although significant numbers remained in use in second-line roles such as VIP transports, air-sea rescue and photo-reconnaissance.[121][122] Strategic Air Command (SAC), established in 1946, used reconnaissance B-17s (at first called F-9 [F for Fotorecon], later RB-17) until 1949.[123][124] With the disestablishment of the US Army Air Forces and the establishment of an independent U.S. Air Force in 1947, most extant B-17s were transferred to USAF.
The USAF Air Rescue Service of the Military Air Transport Service (MATS) operated B-17s as so-called "Dumbo" air-sea rescue aircraft. Work on using B-17s to carry airborne lifeboats had begun in 1943, but they only entered service in the European theater in February 1945, also being used to provide search and rescue support for B-29 raids against Japan. About 130 B-17s were converted to the air-sea rescue role, at first designated B-17H and later SB-17G. Some SB-17s had their defensive guns removed, while others retained their guns to allow use close to combat areas. The SB-17 served through the Korean War, remaining in service with USAF until the mid-1950s.[52][125][126]
In 1946, surplus B-17s were chosen as drone aircraft for atmospheric sampling during the Operation Crossroads atomic bomb tests, being able to fly close to or even though the mushroom clouds without endangering a crew. This led to more widespread conversion of B-17s as drones and drone control aircraft, both for further use in atomic testing and as targets for testing surface-to-air and air-to-air missiles.[127] One hundred and seven B-17s were converted to drones.[128] The last operational mission flown by a USAF Fortress was conducted on 6 August 1959, when DB-17P, AF Ser. No. 44-83684 directed a QB-17G, AF Ser. No. 44-83717, out of Holloman Air Force Base, New Mexico, as a target for an AIM-4 Falcon air-to-air missile fired from an F-101 Voodoo. A retirement ceremony was held several days later at Holloman AFB, after which 44-83684 was retired to the Military Aircraft Storage and Disposition Center (MASDC) at Davis-Monthan Air Force Base, Arizona. Perhaps the most famous B-17, the Memphis Belle, is currently being fastidiously restored to its World War II wartime appearance by the National Museum of the United States Air Force at Wright-Patterson Air Force Base, Ohio.[129]
During the last year of World War II and shortly thereafter, the United States Navy acquired 48 ex-USAAF B-17s for patrol and air-sea rescue work. The first two ex-USAAF B-17s, a B-17F (later modified to B-17G standard) and a B-17G were obtained by the Navy for various development programs.[123] At first, these aircraft operated under their original USAAF designations but on July 31, 1945, they were assigned the naval aircraft designation PB-1, a designation which had originally been used in 1925 for the Boeing Model 50 experimental flying boat.[130]
Thirty-two B-17Gs[131] were used by the Navy under the designation PB-1W, the suffix -W airborne early warning. A large radome for an S-band AN/APS-20 search radar was fitted underneath the fuselage and additional internal fuel tanks were added for longer range, with the provision for additional underwing fuel tanks. Originally, the B-17 was also chosen because of its heavy defensive armament, but this was later deleted. These aircraft were painted dark blue, a standard Navy paint scheme which had been adopted in late 1944.[123][130] The PB-1W eventually evolved into an early warning aircraft by virtue of its APS-20 search radar.[131] PB-1Ws continued in USN service until 1955, gradually being phased out in favor of the Lockheed WV-2 (known in the USAF as the EC-121, a designation adopted by USN in 1962), a military version of the Lockheed 1049 Constellation commercial airliner.
In July 1945, 16 B-17s were transferred to the Coast Guard via the Navy; these aircraft were initially assigned U.S. Navy Bureau Numbers (BuNo), but were delivered to the Coast Guard designated as PB-1Gs beginning in July 1946.[123][126] Coast Guard PB-1Gs were stationed at a number of bases in the U.S. and Newfoundland, with five at Coast Guard Air Station Elizabeth City, North Carolina, two at CGAS San Francisco, two at NAS Argentia, Newfoundland, one at CGAS Kodiak, Alaska, and one in Washington state.[126] They were used primarily for air-sea rescue, but were also used for iceberg patrol duties and for photo mapping. Air-sea rescue PB-1Gs usually carried a droppable lifeboat underneath the fuselage and the chin turret was often replaced by a radome.[126][132] The Coast Guard PB-1Gs served throughout the 1950s, the last example not being withdrawn from service until October 14, 1959.[123][132]
A number of B-17s were used by the CIA front companies Civil Air Transport, Air America and Intermountain Aviation for special missions. These included B-17G 44-85531, registered as N809Z. These aircraft were primarily used for agent drop missions over the People's Republic of China, flying from Taiwan, with Taiwanese crews. In all, four B-17s were shot down in these operations.[133]
In 1957 the surviving B-17s had been stripped of all weapons and painted black. In mid-September, one of these Taiwan-based B-17s was flown to Clark Air Force Base in the Philippines. assigned for covert missions into Tibet. Two missions into Tibet are known to have been flown by this B-17G (44-85531).
On 28 May 1962, N809Z, piloted by Connie Seigrist and Douglas Price, flew Maj. James Smith, USAF and Lt. Leonard A. LeSchack, USNR to the abandoned Soviet arctic ice station NP 8, as Operation Coldfeet. After parachuting from the B-17, Smith and LeSchack searched the station for several days. On 1 June, Seigrist and Price returned and picked up Smith and LeSchack using a Fulton Skyhook system installed on the B-17.[134] In 1965, N809Z was used to perform a Skyhook pick up in the James Bond movie Thunderball. This aircraft, now restored to its original B-17G configuration, is now on display in the Evergreen Aviation & Space Museum in McMinnville, Oregon.
The B-17 was a versatile aircraft, serving in dozens of USAAF units in theaters of combat throughout World War II, and in non-bomber roles for the RAF. Its main use was in Europe, where its shorter range and smaller bombload relative to other aircraft available did not hamper it as much as in the Pacific Theater. Peak USAAF inventory (in August 1944) was 4,574 worldwide.[62]
The B-17 Flying Fortress has become, for many reasons, an icon of American power and a symbol of its Air Force. During the 1930s, the USAAC, as articulated by then-Major General Frank Maxwell Andrews and the Air Corps Tactical School, touted the bomber as a strategic weapon.[136][N 5]General Henry H. Arnold, Chief of the Air Corps, recommended the development of bigger aircraft with better performance and the Tactical School agreed completely.[137][N 6]
When the Model 299 was rolled out on 28 July 1935, bristling with multiple machine gun installations, Richard Williams, a reporter for the Seattle Times coined the name "Flying Fortress" with his comment "Why, it's a flying fortress!".[138] Boeing was quick to see the value of the name and had it trademarked for use. In 1943, Consolidated Aircraft commissioned a poll to see "to what degree the public is familiar with the names of the Liberator and the Flying Fortress." Of 2,500 men in cities where Consolidated adverts had been run in newspapers, 73% had heard of the B-24 Liberator, while 90% knew of the B-17.[7]
After the initial B-17s were delivered to the Air Corps 2nd Bombardment Group, they were used on promotional flights emphasizing its great range and navigational precision. In January 1938, group commander Colonel Robert Olds flew a YB-17 from the east to west coast, setting a transcontinental record of 13 hours 27 minutes. He also broke the west-to-east coast record on the return trip, averaging 245 mph (394 km/h) in 11 hours 1 minute.[139] Six bombers of the 2nd Bombardment group took off from Langley Field on 15 February 1938 as part of a goodwill flight to Buenos Aires, Argentina. Covering 12,000 miles (19,000 km) they returned on 27 February, with seven aircraft setting off on a flight to Rio de Janeiro, Brazil, three days later.[140] In a well-publicized mission on May 12 of the same year, three B-17s "intercepted" and took photographs of the Italian ocean liner SS Rex 610 miles (980 km) off the Atlantic coast.[141][N 7]
During the war, the largest offensive bombing force, the Eighth Air Force, had an open preference for the B-17. Lieutenant General Jimmy Doolittle wrote about his preference for equipping the Eighth with B-17s, citing the logistical advantage in keeping fielded forces down to a minimum number of aircraft types with their unique servicing and spares. For this reason, he wanted B-17 bombers and P-51 fighters for the Eighth. His views were supported by Eighth Air Force statisticians, whose studies purportedly showed that Fortresses had utility and survivability much greater than that of the B-24.[7] Making it back to base on multiple occasions despite extensive battle damage, its durability took on mythical proportions;[5][6] stories and photos of B-17s surviving battle damage were widely circulated during the war.[7] Despite an inferior performance and bombload compared to the more numerous B-24 Liberator,[142] a survey of Eighth Air Force crews showed a much higher rate of satisfaction in the B-17.[143]
Hollywood featured the airplane in its movies, such as Twelve O'Clock High starring Gregory Peck.[144] This film was made with the full cooperation of the United States Air Force and made use of actual combat footage. In 1964, the movie was made into a television show of the same name and ran for three years. Footage from Twelve O' Clock High was also used, along with three restored B-17s, in the 1962 film The War Lover. The B-17 also appeared in the 1938 movie Test Pilot with Clark Gable and Spencer Tracy, with Clark Gable in Command Decision in 1948, in Tora! Tora! Tora! in 1970, and in Memphis Belle with Matthew Modine, Eric Stoltz, Billy Zane, and Harry Connick, Jr. in 1990. The most famous B-17, the Memphis Belle, toured the U.S. with its crew to reinforce national morale (and to sell War Bonds), and starred in a USAAF documentary, Memphis Belle: A Story of a Flying Fortress.[145]
Many B-17 crew members received military honors and 17 received the Medal of Honor, the highest military decoration awarded by the United States:[149]
Data from The Encyclopedia of World Aircraft[33]
General characteristics
Performance
Armament
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