Boeing B-17 Flying Fortress
Four-Engined Heavy Bomber Aircraft
The legendary Boeing B-17 Flying Fortress accounted for over 290,000 sorties with 640,000 tons of ordnance dropped during World War 2.
Authored By: Staff Writer | Last Edited:
While the Consolidated B-24 Liberator four-engined heavy bomber dropped more war tonnage and was built in greater numbers, the Boeing B-17 "Flying Fortress" four-engined "heavy" left a longer lasting memory on American military aviation history for its part in World War 2 (1939-1945). The aircraft was a primary component of the famed Eight Air Force ("The Mighty Eighth") as it took over daytime bombing operations over Europe in the march to Berlin - amassed forces launching from airfields all over England. In time, the fortunes of war began to favor the Allies as the Third Reich's territories began to shrink - first from Italy and then from France and the Low Countries. The bomber made a name for itself as a workhorse component and was the subject of many war bond drives back in the United States to help drum up continued support of the war effort. Before the end, the Kingdom of Italy, Germany, and the Empire of Japan would all be defeated in full - each nation having tasted as least some of what the Boeing product could offer. Many of the line continued in service after the war with foreign players while many more were sent to the scrap heap after their flying days were over - leaving few in operational condition today.
For its contribution in the Grand Conflict, the B-17 accounted for nearly 300,000 total sorties against enemy targets and dropped a staggering 640,000 tons of bombs. It helped to refine American bomber doctrine that needed attention even prior to the start of the war and led to the development of another classic multi-engined platform of the conflict - the Boeing B-29 "Superfortress" (detailed elsewhere on this site). At the start of the Eighth Air Forces commitment in Europe, several hundred B-17s could be seen making up one bomber flight but, before the end of the war in 1945, the enemy was being pummeled into oblivion by what would become thousands of individual bombers making up wave-after-deadly wave of formational flying.
It was this kind of determination on the part of the Allies that led to an unrelenting bombing campaign - the Americans to handle the daylight duties and the British to enact their own brand of bombing justice in the low-light hours. Such attention to enemy targets eventually led to much destabilization of enemy infrastructure - disrupting supply lines, damaging key industry, and - of course - lowering pro-war morale. As the B-17 made a name for itself over Europe, the B-24 - of similar over-battlefield function - also made its case as another of the classic heavy American bombers of the war - its commitment eventually graduated from European airspaces to that of the Pacific Theater against the might of the Empire of Japan.
Flying Fortress Crews
A single flying fortress required the specialties of multiple, specially-trained crewmen. Some were charged with its flying, others with its repair, and still others with its defense. Depending on the model, the crew total could range up to ten personnel. The bombardier was positioned at the extreme front-end of the fuselage with a commanding view of the action ahead. A seat and the all-important bombing equipment was fitted here. Immediately behind him was the navigator whose station allowed paper maps to be splayed out for navigating the bomber to its expected location. A seat and light were allotted to this position for some creature comforts. The two pilots sat side-by-side above and behind the nose section with a clear view of both engine pairings located at each wing mainplane. A passageway located under the cockpit floor allowed crewmembers to reach the nose compartment as needed. Directly behind and above the flightdeck was the dorsal turret manned by a single operator - typically the aircraft's in-flight engineer.
Aft of the cockpit was the bomb bay with a plank set across the chasm for accessing the further rear of the aircraft. From this passage was the radio operator's station and, again, this was a seated position complete with tabletop that held the aircraft's communication's center (the radioman's position originally contained an upward-firing, trainable machine gun but this was deleted in later production models). Aft of the radioman was the ball turret (this was model dependent however) set into the floor of the fuselage offering excellent traversal under and around the aircraft's vulnerable underside. A pair of waist (or beam) gunners manned machine guns at the midway point of the empennage's length. The tail gunner (again, this position depended on the production model) was rather segregated at his station which was found at the extreme end of the fuselage.
Crewmen were called to operate in noisy, smelly, and utterly drafty conditions at altitudes that would freeze exposed skin. As such, fleece-lined flight suits were the norm as were oxygen supplies for breathing in the thin air. Individual comm systems allowed the crew to communicate with one another. No pressurization was possible with the crew spaces of the Flying Fortress.
Flying Fortress Development
The Flying Fortress had its roots set in the 1930s as the world seemingly geared up for another lengthy and bloody World War. "Strategic Air Power" was being formulated by the United States Army Air Corps (USAAC) which, at the time, operated both the land-based Army component as well as the air service section under one banner. Tactical bombers (typically light and medium classes) were called against smaller, more defined enemy targets often operating closer to the front lines while strategic bombers were to take the long-range approach and strike at enemy targets deep within enemy-held territory. The latter operation would require aircraft of some capability, particularly in range/endurance as well as a useful bombload capacity to make the trip worthwhile. Once over the target, accuracy over the target became another important quality.
In 1933, "Project A" was arranged under secrecy by authorities of the USAAC and Boeing managed to secure a deal by way of its XB-15 heavy bomber design. The XB-15 (detailed elsewhere on this site) very much mimicked the form and function of the future B-17 as its four engines were spread across wide-spanning wing mainplanes, the nose was glazed over, and the cockpit being stepped. The tail unit was conventional and "blisters" set off the waist gunner positions while a dorsal turret was overhead present towards the nose. The wings were so large and relatively deep that flight engineers could enter the structures to make on-the-spot repairs/adjustments of engines in-flight with access provided by passageways. At the time, the XB-15 marked the largest aircraft ever built by the Americans and went on to be a record-setter under some related class categories. Power was from 4 x Pratt & Whitney air-cooled radials and the crew numbered ten.
The XB-15 beat out Martin's XB-16 proposal which was to carry 4 x Allison V-12 liquid-cooled inline engines and a also feature a crew of ten. It is noteworthy that the USAAC was not all that interested in inline engines at this time - there being some exceptions such as the Curtiss P-40 Warhawk and Bell P-39 Airacobra fighters. In time these would be joined by the Lockheed P-38 Lightning and the North American P-51 Mustang fighters.
While the XB-15 was something of a technological marvel for the time, it was deemed obsolete by the time it recorded its first-flight on October 15th, 1937 and the program was eventually cancelled with just a single flyable prototype completed. This form was evolved into the Y1B-20 by Boeing but this model was never built by the company as it was also cancelled after 1938. Nevertheless, the two aircraft were influential in the development of the B-17 and its equally-storied successor, the B-29 "Superfortress" - forever cementing Boeing as a competent large aircraft-maker.
Even before the death knell was struck on the earlier Boeing products, company engineers had already been working on a refined heavy bomber concept that became the "Model 299" and this offering now competed directly with Douglas' own "DB-1". The USAAC requirement, now more refined after some years in existence, sought a heavy, multi-engined bomber-type capable of long distance travel with a full 2,000lb bomb load. The aircraft would be able to reach speeds between 200 and 250 miles per hour and range out to 2,000 miles. The four engines became a requirement for such a design and was highly favored for all heavy bomber forms during this time period - offering the necessary power to take-off, make the flight under full load, and eventually return home. Interestingly, the USAAC considered the heavy bomber to fulfill the primary role of "coastal defender" and to be sent to attack inbound enemy ships nearing American shores.
Design of the Model 299 was credited to a Boeing team headed by Edward Curtiss Wells and was a originally private venture initiative by the company which had yet to secure a formal USAAC development contract. The prototype was fitted with 4 x Pratt & Whitney R-1690 "Hornet" air-cooled engines driving three-bladed propeller units with the nacelles set in pairs at the rounded wing mainplanes which were, themselves, set low along the fuselage sides. The aircraft's finish was in all-metal (silver), giving it a futuristic appearance. A tricycle undercarriage was used for ground-running and gave the product a pronounced "nose-up" posture which limited pilot vision but was accepted practice in the world of aviation for the period. The nose was heavily framed at the bombardier's position and provided the crewmen with a good view of the forward action (arguably the best vantage point among the crew). Various window ports were set along the fuselage and the cockpit took its usual place above and behind the nose. The tail unit incorporated a single vertical fin and low-set horizontal planes.
During the rollout of this aircraft, it is said that a journalist present at the ceremony commented on the bomber as a "flying fortress" and the name apparently stuck with Boeing and its Model 299 when it entered service. The prototype made its maiden flight on July 28th, 1935 and official Army testing followed at Wright Field in Ohio during the latter part of that year. At this time, the Model 299 had been given the USAAC experimental designator of "XB-17".
The project suffered a setback during October of that year when the prototype crashed, killing several of the crew. Despite this, the USAAC ordered thirteen of the bombers in January of 1936 and graduated the design to the developmental designation of "Y1B-17". The first of this form appeared before the end of the year in December. Boeing added the Model 299F for the USAAC as a static air frame which the service took on as the "Y1B-17A". This model then graduated to become a flyable version as the "B-17A". With a revised nose section, enlarged control surfaces, and 4 x R-1820-51 radial engines of 1,200 horsepower, the Model 299M fulfilled the B-17B designation and thirty-nine aircraft were ordered in 1938 to the standard to continue testing under more realistic operational conditions. Another key switch was the shift from pneumatic braking to hydraulic.
World War 2 Arrives
The arrival of World War 2 in Europe on September 1st, 1939 pushed the American military network into action for the inevitable defense of the United States homeland as well as its overseas territories. As such, during 1940, the USAAC moved to order eighty B-17C/D models from Boeing's Model 299H design and these carried improved armoring, self-sealing fuel tanks, and increased defensive armament. The mark carried R-1820-65 series radials while the beam blister gun positions were replaced by teardrop-shaped shrouds for reduced drag. A gondola-type "bathtub" turret succeeded the ventral gun blister. It was these forms that the British took into service during the early part of the war under the Lend-Lease Act of 1941. British B-17s were named "Fortress" followed by the variant designations (Mk.1, Mk.2, Mk.3 and so forth). The USAAC was quite hesitant to hand over its new bomber to a foreign party for it wished to shore up its own limited heavy bomber stock.
The USAAC becomes the USAAF
In June of 1941, the USAAC was officially rebranded as the United States Army Air Forces (USAAF) and under this banner there were several distinct air services operating (hence the word "Forces" in the title). Each of these sub-services was charged with defense of a particular patch of global real estate. At present, the USAAC could call on fewer than 200 B-17 bombers and these were quickly shipped overseas to help thwart attacks on American overseas territories - namely those found in Hawaii and the Philippines (the Empire of Japan, and its military-driven expansionism, was the United States' most immediate threat in the pre-war period).
After some practical usage, the B-17 was soon found to lack adequate rearward-facing defensive armament. British bombers were mauled from the rear by German Luftwaffe Bf 109 fighters with little resistance so this led Boeing to answer with the Model 299O, the B-17E in service, which introduced the twin-gunned tail position overlooking the action directly to the rear of the aircraft. Firing arcs were limited but the guns were better than nothing at this critical section of the aircraft. They were, however, improved with the "Cheyenne" installation in soon-to-come B-17G models which offered a greater field-of-fire and as well as improved gun-laying. The gunner's station was positioned directly under the vertical tail fin and between the horizontal planes.
Like the belly turret gunner, the tail gunner made his way to his station only after the aircraft was in flight and connected to his oxygen supply and intercom system. He took on a kneeling position (sitting on his legs) during action - which was not the most comfortable over hours of scanning the skies.
Boeing would go on to build 512 of the E-model forms (from its Seattle plant) before the end of the run and this variant was monumental for the series at it became the first to see consistent operational service (including combat exposure). Its importance early-on cannot be understated as the platform was used as a deterrent as much as it was a bomb delivery system. For the early part of 1942, a few were beginning to be stationed on Australian soil in preparation for Japanese incursions in and around Australian territory across the South Pacific. By the middle part of that year, the E-models were arriving in England to shore up the Allied bomber arm over Europe as well.
Evolution of the line did not stop with the E-models for, in April of 1942, the B-17F quickly arrived based on Boeing's Model 299P design. This carried 4 x Wright R1820-97 "Cyclone" air-cooled radials of 1,380 horsepower each which improved higher-altitude performance and increased range, the latter made possible by the inclusion of what came to be known as "Tokyo Tanks". Defensive armament was once-again addressed: as the tail turret proved instrumental in deterring enemy fighters from attacking the rear of the heavy bomber, a "ball" turret was now added to the ventral line of the aircraft. This addition encompassed a ball enclosure which encapsulate the machine gunner who managed a pair of heavy machine guns. With feet placed into stirrups and a simple belt holding him in place, the small-statured gunner was expected to defend the bomber from threats emerging below the belly. Ammunition fed to each gun from outside the ball though within the fuselage and access to the ball turret was by a hatch. Power to the system was electrical.
Beyond the engines and ball turret, the F-model was notable in bringing about a single-piece plexiglass nose cone which did away with the complex, heavily-framed unit of earlier production models. This gave the bombardier one of the most impressive views from the aircraft as he was able to see through an unobstructed pane over all of the forward field of the bomber - very useful in identifying ground-based target areas for his role.
These changes led to a greater overall weight for the heavy bomber but this was acceptable amidst the growing demands of the war. The F-models took over production lines from the now-abandoned E-models and 3,405 units were added to the B-17 stable - Boeing contributed 2,300 aircraft while 605 arrived from Douglas Aircraft plants, and a further 500 came from Lockheed Vega facilities - a joint effort to be sure.
The B-17 Comes of Age - the Definitive B-17G
The evolution of the B-17 was fast and furious with much owed to the evolution of the war itself. The B-17G model was a major upgrade over previous versions and became the undisputed definitive form of the series. It carried over the refinements of the improved F-models mentioned earlier but also introduced the twin-gunned, electrically-powered Bendix chin turret for the bombardier's position. One of the lingering limitations of the defensive network of earlier B-17s was its defense against oncoming attacks by enemy fighters. There were "cheek" machine guns the bombardier and navigation could rely on as well as some support from the dorsal turret but these held restricted firing arcs when concerning direct frontal threats. The Bendix installation gave unrestricted access to the forward field of the aircraft and could scan across the horizon for threats side-to-side. German pilots were, no doubt, surprised that their frontal attacks were no longer useful and, instead, greeted with hot lead from twin 0.50 caliber Brownings.
Beyond this armament improvement came an increased war load capability: the bomber now capable of carrying up to 90,000lb of conventional drop stores over distance. Boeing contributed 4,035 G-models while Douglas added 2,395, and Lockheed Vega another 2,250 units.
The B-17 In Action
B-17 Flying Fortresses followed common bomber doctrine of the time in that the units were arranged in what was known as a "box formation". This formation, made up of multiple individual bombers flying within relatively close proximity to one another, allowed virtually every machine gunner onboard the respective aircraft to bring their guns to bear against any impending threat as needed through combined firepower. With no fewer than twelve machine guns featured on a single G-model, a sole B-17 was quite the defensive network for enemy fighters to get through during an attack run.
Gunner positions on a B-17G model included 2 x 0.50 caliber machine guns in the Bendix chin turret, 1 x 0.50 caliber machine guns at each cheek position, 2 x 0.50 caliber machine guns at the dorsal turret, 2 x 0.50 caliber machine guns at the ventral ball turret, 1 x 0.50 caliber machine guns at each beam position, and 2 x 0.50 caliber machine guns at the tail position. In theory, no one approach route outside of the bomber was uncontested. All positions were afforded some level of armor protection but this varied considerably by position.
The Norden Bombsight
One of the major challenges of bombing in the 1930-1940 period was accuracy and there were several technological attempts made to aid the bombardier in his role but none were as critical to the war effort as was the Norden Bombsight designed by Carl Lukas Norden - who previously had worked for the Sperry Gyroscope Company before World War 1 (1914-1918). Lucas first interested the United States Navy (USN) in his invention as the service sought to increase the lethality of its own bombers against moving enemy warships. The early-form Mk III bombsight was developed in 1921 from this requirement and the design eventually progressed to the M-Series units which were adopted in 1943.
The bombsight was instrumental in gradually increasing accuracy of American bombers and this improved from a near 25% accuracy (within 1,000 yards) to about 40% (within 500 yards) by 1944 and beyond. The bombardier was also allowed lateral control of the aircraft from the pilot during the bombing run which further gave aided the bombardier in placing the ordnance where it had to go. Bomber flights frequently followed a lead plane as their "director" and would drop war loads on queue. As such, the lead bombardier was to make absolutely sure he was over the correct target and this was accomplished by studying photography and maps for hours on end to verify physical structures and landmarks. During the bomb run itself, there were also the pressures of Flak attack, enemy fighter drives, and the like - external distractions not properly replicated in training. His job was made easier by a competent navigator whose primary role was to get the bomber to within range of the target by way of maps and measurements. The pilots fed off of the navigator's direction and the radioman aided the effort as well. In this way, the entire B-17 core crew was required to reach some level of cohesion for not only mission success but also unit survival.
About 40,000 candidates graduated from the USAAF bombardier program related to use of the ultra-secret Norden bombsight system.
The B-17 Cockpit
The pilot and co-pilot sat in the cockpit in a side-by-side arrangement with engine/throttle controls seated between them - offering equal control access. Each pilot also had a good view of his respective engine pairing for monitoring against fires and general failures. Either pilot could also control the aircraft as needed through their control yokes which was particularly useful should one crewman become incapacitated or killed during a mission. Views out-of-the-cockpit were generally adequate but restricted on the whole - ground-running certainly required the assistance of ground personnel for direction.
The B-17 quickly became recognized for its ability to sustain an extraordinary amount of combat punishment and keep flying. This is not to say that the design was invulnerable to enemy attack - for many B-17 bombers and B-17 bomber crews lost their lives during the war - but the Boeing product was known to limp back home with even entire sections of aircraft missing. Whole sections of tail unit could be shot away or the fuselage blown open or severed to the point of nearly falling off but the Boeing bomber continued to "bring the boys home" time-and-time-again. While fighters were one direct threat, the seemingly random nature of ground-based FlaK fire were terrifying for the bomber formations required to hold course while entering into what was essentially an aerial minefield. When the enemy interceptors stopped attacking the Fortress, this was a sure sign that an extensive FlaK attack was to follow.
Despite all of the dangers, B-17 crews did their jobs successfully throughout the entire course of the war. This led the bomber to become a symbol of American aerial might over its enemies and was the principle component in the dismantling of the Reich's war-making capability into 1945. A flight of thousands of such bombers became commonplace heading into the final year of the war and the German nation capitulated under pressure from all sides by May of that year, signaling the end of the war in Europe. B-17s also did their part in the Pacific Theater and ultimately paved the way for the high-flying Boeing B-29 "Superfortress" which eventually dropped the atomic bombs on Hiroshima and Nagasaki to help end the war in the East.
B-17 Post-War Exposure
Total production of B-17s reached 12,731 units by war's end. Production spanned from 1936 until 1945. Beyond the United States and Great Britain, the B-17 was taken into service by a plethora of global operations mainly during the post-war years and these were used in both military and civilian markets. Operators ranged from Brazil, Canada, and Columbia to Portugal, the Soviet Union, and the Republic of China.
During the war, those B-17s operating in the Far East and unable to return to American bases in the region for one reason or another were forced to land on Soviet soil and these specimens were interned and reengineered by the Soviets down to the last bolts. This jumpstarted the Soviet bomber program of the Cold War period and resulted in types like the Tupolev Tu-4 which took over for the refurbished B-17s in Soviet service. Soviet B-17s operated into 1948.
Similarly during the war, the German regime captured as many as forty B-17s in various conditions and refurbished them back into fighting form. These were known locally as the Dornier Do 200 and used in reconnaissance and general spying roles through Luftwaffe unit KG 200.
When Israel was formed as a nation in 1948, it took on three B-17s when establishing its newly-founded air service. The specimens were obtained through Czech and South American sources and were pressed into combat during the 1948 Arab-Israeli War as the subsequent 1956 Suez Crisis, the fleet flying into 1958.
Notable Projects and Offshoots
While there proved many derivatives of the base B-17 design throughout its storied career, two were notable in their attempts - the XB-38 and the XB-40, both based on the established framework of the original B-17 (and both detailed elsewhere on this site). The XB-38, based in the B-17E model, was an attempt to develop an inline piston-engined form of the Flying Fortress to maximize performance of the heavy bomber. 4 x Allison V1710-89 12-cylinder units of 1,425 horsepower each replaced the typical air-cooled radials during the program and this allowed streamlined engine nacelles to be used for better aerodynamics. While performance was, in fact, improved, the sole prototype was consumed by fire in a June 1943 test which ended its flying days. This fire, and the arrival of F-models production units as well as the Allison inline engines being required elsewhere, all contributed to the end of the XB-38.
The XB-40/YB-40 was an F-model B-17 modified by Lockheed Vega to serve as a flying "Gun Bus" reminiscent of World War 1 types intended to escort vulnerable bombers into contested airspace. This was developed prior to jettisonable fuel drop tanks being adopted and longer-ranged escort fighters being available in number. Armament was variable on these aircraft due to their developmental status and some twenty-five aircraft emerged from the program. The Gun Bus variant included extra 0.50 caliber machine guns as well as automatic cannons to go along with improved crew station armoring. Some carried multiple dorsal turrets and individual twin-gunned positions.
The "improvements" led to an aircraft that was heavier by some 4,000lb when compared to a fully-laden B-17 bomber. Decreased performance due to weight gains and added drag, as well as the arrival of long-range P-51 Mustang fighters as escorts, all contributed to the death of the B-17 Gun Bus project. However, these gunships were used in operational service (though for only a short time) with the first mission flown in May of 1943. it was found that these gun-laden heavies had trouble keeping up with the formations once the bombers had dropped their loads. The XB-40/YB-40 program was ended in August of 1943.
The C-108 was the B-17 converted to serve in the transport role. General Douglas MacArthur's own C-108, named the "Bataan", became the most famous of these and was used in the VIP transport role across the Pacific Theater until war's end. The fleet was made up of E- and G-models and some were sent over to the United States Coast Guard service to operate in the Search and Rescue (SAR) role over water. These forms was additionally outfitted with radar for the task.
The B-17 was instrumental in the development of another Boeing product, the Model 307 "Stratoliner", a passenger-hauler introduced in July of 1940 with Pan American Airways. Just ten of these transports were completed but the series operated into 1975.
Beyond these were G-model inspired troop transports, drone aircraft, static and flyable test articles, a missile carrier (MB-17G), reconnaissance platforms (RB-17G), a lifeboat-equipped model (SB-17G), trainers, and an AWACS form (PB-1W) - such was the versatility of the aircraft.
Notable B-17 Bombers
Due simply to the sheer number of B-17 bombers built, and their constant exposure to combat in World War 2, it was only natural that many of the type went on to have highly publicized careers - the most famous of the these becoming the "Memphis Belle". A few notables of the bomber line are briefly detailed below:
Memphis Belle - The Memphis Belle, named after Margaret Polk of Memphis, Tennessee (who was then the girlfriend of the bomber's pilot, Lt. Robert Morgan), carried the iconic nose art of a leggy woman with her face turned away from the viewer (she wore blue on the portside of the forward fuselage and was depicted in red along the starboard side). She was painted by artist Tony Starcer of the 91st Bombardment Group onto the nose of a B-17F. The bomber is notable in being recognized as the first B-17 Flying Fortress to have completed a tour of 25 combat missions which meant that the crew had earned the right to return stateside for good (the aircraft also claimed eight air victories against the Luftwaffe in that time frame). The Belle went on to serve in war bond drives and the like during the conflict and ultimately ended in the care of the National Museum of the United States Air Force (Dayton, Ohio). A Hollywood version of the true story of the Memphis Belle appeared as a motion picture in 1990 (the bomber was played by the still-flying B-17G "Sally B"). During the war in 1944, the aircraft was also the subject of the 45-minute-long documentary "Memphis Belle: A Story of a Flying Fortress" which was meant to depict the final mission of the bomber (in reality it was actually the second-to-last mission flown).
Hell's Angels - The Hell's Angels was a B-17F named after the 1930s Howard Hughes movie "Hell's Angels". By January of 1944, this bomber had completed 48 total missions and she and her crew were sent stateside to drum up support for the war effort. She ended her days in March Field (California) to serve as a crew trainer from May of 1944 onward. Unfortunately this Flying Fortress was not saved from the scrap heap.
The Swoose - The Swoose operated from April 1941 until February of 1944 and went on to be preserved - the only one of the earlier B-17D models to be saved and of note being its distinct "shark fin" vertical tailplane. The Swoose operated from the first day of the U.S. entry into World War 2 (December 1941) and managed to survive the war intact. After suffering through periods of exposure to weather and damage (the latter at the hands of lowly vandals), the aircraft was saved for preservation work by the National Museum of the United States Air Force (Dayton, Ohio).