The B-17 Flying Fortress

The Flying Fortress that bombed Fortress Europe

Ask a World War II buff to name a heavy bomber, and they're guaranteed to say the Flying Fortress. It was neither the largest, nor the fastest, the most produced, the one with the longest range or the heaviest payload; but it is the single most iconic warplane of its category. Best known for the daylight bombing campaign over Nazi-occupied Europe, the B-17 also served in the Pacific and with the Royal Air Force (RAF). Even less well-known is the fact that the very first prototype crashed during testing, almost nipping the story of the war's most famous bomber in the bud.

The story of the Flying Fortress began in 1934, when U.S. Army Air Corps put out a proposal for a replacement to its previous heavy bomber, the Martin B-10. The B-10 first flew two years earlier, and was very modern at the time with an all-metal body and monoplane wings, but aircraft design was advancing in leaps and bounds, and the military already saw the need for something even better. They wanted something that could carry a "useful bombload" at 10,000 ft (3,000 m), flying at least 200 mph (320 km/h) for 10 hours. It wasn't a strict requirement, but a range of 2,000 miles (3,200 km) and a speed of 250 mph (400 km/h) was considered desirable. Contestants were to build prototypes at their own expense, and the tests were to be held at Wilbur Wright Field in Dayton, Ohio.

Three entries were submitted. The Glenn L. Martin Company's Martin 146 and the Douglas Aircraft Company's DB-1 both had two engines; Boeing went in a different direction. They had a very modern airliner, the Model 247, but realized that a bomber conversion would not stand up to the rigors of the war. They also had a single prototype of the XB-15, a massive four-engine bomber that was never adopted and eventually converted into a cargo plane. Boeing decided to combine the two designs: build something of a more reasonable size than the XB-15, but still powered by four engines, which would hopefully give it great performance.

The prototype, Model 299, got the nickname "Flying Fortress" a day before its first flight in June 1935, when a reporter inspired by its armament of five .30 caliber machine guns described as a "15-ton flying fortress" in a photo caption. The company quickly adopted and trademarked the name. The plane flew from Seattle to Wright Field in 9 hours and 3 minutes with an average speed of 252 mph, which was very respectable at the time. As mentioned above, it was armed with five .30 caliber machine guns (Read our earlier article): one in the nose, one in dorsal (top) and ventral (bottom) mountings (though notably not turrets – they didn't have a full arc of fire), and two in side blisters around the waist. The plane arrived to no reception whatsoever by the Air Corps, as officials didn't expect it for at least another hour.

Model 299 performed spectacularly in comparison with the two-engine prototypes; both then-Army Chief of Staff Douglas MacArthur (Read our earlier article) and General Headquarters head Frank Maxwell Andrews supported the use of large, long-range four-engine bombers. But even with this support, the B-17's career was almost cut short by an accident. On one test flight, the pilot and the copilot forgot to disengage the gust lock, a device that kept control surfaces in position on the ground to protect them from damage in strong wind. With the lock still in place, the plane took off, its nose pointed sharply upwards, then went into a stall and crashed, killing two of the five men onboard. The silver lining of the tragedy was the development of a new protocol: the written pre-flight checklist, which is now mandatory on all aircraft.

The crash disqualified Model 299 from the testing. The Air Corps still wanted the B-17, but the Army balked, both at the accident, and its high price tag – it cost 1.7 times as much as the Douglas entry. The Douglas DB-1 was chosen and went into service as the B-18 Bolo, but proved unsuitable during the war.

The Air Corps found a loophole to keep developing the B-17. They were allowed to buy 13 planes for testing purposes, and used that allotment on Flying Fortresses. These started appearing at military exercises, air shows and aerial demonstrations, establishing the bomber in the public consciousness. U.S. military thinking at the time was still influenced by isolationist policies and defensive strategy: the role of bombers was imagined to fly out and destroy enemy ships heading towards the American mainland or overseas territories such as Hawaii or the Philippines. In May 1938, B-17s flew 610 miles (980 km) offshore to "intercept" the Italian ocean liner Rex. The successful demonstration proved the plane's ability to serve America's strategic goals, and infuriated the Navy, which was scared that it might be toppled as the country's first line of defense. Army resistance against the B-17 had faded by this point, allowing the Air Corps to order more.

The Flying Fortress first saw combat in small numbers in July 1941 with the RAF, which did not yet have British-built heavy bombers in sufficient numbers at the time and relied on Lend-Lease (Read our earlier article). These were the B-17C models, named "Fortress Mk.I" in British service. These had the waist gun blisters replaced by Perspex window panels, the ventral gun mounting was changed to a gondola nicknamed the "bathtub turret," and had self-sealing fuel thanks and armor plates added. 

This early version proved unsuccessful in daytime bombings, and, in fact, high losses among Fortresses was the reason Bomber Command adopted a night bombing strategy. The mission also revealed numerous weaknesses that were fixed in later versions: mechanical and electrical problems, crew fatigue, guns icing over at high altitudes, and the plane likely catching on fire after a hit. British B-17s (including later models) were relegated first to long-range maritime patrol and anti-submarine missions, then later to meteorological reconnaissance in the north. (Read our earlier article) Late in the war, some of the more modern versions of the B-17 flying with the RAF were outfitted with the "Airborne Cigar" (or ABC) electronic countermeasure system. These planes were interspersed along bomber streams during night attack and jammed German radio frequencies, preventing German radar operators from guiding night fighters to the bombers.

B-17s saw action on December 7, 1941, the first day of direct U.S. involvement in World War II. 12 B-17s heading from American to the Philippines stopped at Hawaii for refueling – and arrived as the Japanese attack was happening. Coming under fire, they quickly diverted from Hickam Field to Bellows Field and landed, losing two planes in the process.

The B-17s already in the Philippines already had plans for a Japanese attack, and were supposed to take off and bomb Japanese airfields in Formosa (Taiwan today). Amid confusing and false reports of enemy attacks,  MacArthur delayed the mission, allowing the Japanese to destroy half of the force on the ground in a single attack, and eliminate the rest in the next couple of day.

The Pacific was generally not kind to the B-17. The bomber could fly too high for most A6m Zeros to intercept, but high-altitude bombing proved inaccurate against maneuvering Japanese ships. Low-altitude attack skipping bombs on the water enjoyed some success, but B-17s were mainly used to search and rescue in the later years of the Pacific war.

Development of the Flying Fortress continued throughout the war. The B-17D introduced numerous minor improvements, and upgunned the plane: it had two .50 cal machine guns (Read our earlier article) in both the dorsal and ventral mounts, and one each in the waist positions. The bomber still lacked any rear firepower, allowing German interceptors to attack it with relative impunity.

The B-17E finally added a pair of .50 cal machine guns in a tail turret. It also added a dorsal turret and replaced the ventral gun position with the famous Sperry ball turret, giving the plane more rear firepower. The ball turret could be jettisoned before a crash landing; this was important, since a belly landing with the turret still in place was likely to break the plane's back, increasing the chances of it being unrepairable.

The increased rear firepower, and the fact that U.S. heavy bombers started flying in complex "combat boxes" to cover each other with their guns, forced the Germans to adapt. The B-17's nose still only held a single .30 gun, making frontal attacks a relatively safe option for the Luftwaffe. (Read our earlier article) The B-17F, besides increasing bomb capacity to 8,000 lb, adding "Tokyo tank" fuel tanks in the wings for increased range, and getting more powerful engines, also added more guns to stave off fighters. The type experimented with various numbers and arrangements of .50 cal guns in and near the nose, but the eventual solution came from an otherwise failed experiment.

With the U.S. Army Air Forces still lacking effective long-range escort fighters like the P-51 Mustang (Read our earlier article), they experimented with turning some B-17s into gunships that carried no bomb load, but was given an extra heavy gun armament to protect other bombers. 25 of these "YB-40" gunships were built. They carried a varying number of machine guns, commonly around 18 but also going up to 30 in a few cases, and could even mount 40 mm guns. The design was still considered a failure, as the planes were extremely heavy and couldn't keep up with regular B-17s which no longer carried bombs on the way home. However, one innovation of the YB-40 was adopted for "normal" Flying Fortresses: a pair of "cheek" machine guns were added to the sides of the nose, which, along with a pair in the chin turret under the nose, gave the bomber significant forward firepower. The final combination of cheek and chin turrets started appearing on the last production runs of the B-17F. The 3,405 B-17Fs built made up a quarter of the total 12,731 Flying Fortresses.

The 8th Air Force mainly relied on the B-17F during its effort to cripple Germany's air force over Europe. Escorted by recently introduced long-range fighters, they would fly missions over Germany, forcing the Luftwaffe to launch interceptors, which would then be shot down by the escorts. The strategy worked, and while flak still took its toll, bomber losses were so low by the spring of 1945 that no more replacements were sent as they were deemed unnecessary.

The one type that outnumbered the B-17F the B-18G, was the last production model, and the definitive version with 8,680 made, two-thirds of the total production. Both the cheek and waist guns were staggered, with one slightly ahead of the other, to make the interior less cramped. In fact, one of the two waist gunners was usually given a different job. Late in the war, only the lead bombers of a formation actually had the bombardier aim at the target, while the other planes just dropped their own load when the lead plane did. This meant that most B-17s no longer had a need for a bombardier. One of the waist gunners was sent up to the front to man the chin turret and release the bomb when the lead Fortress did, while the other waist gunner was left in the waist to handle both turrets.

Several nations beside the U.S. and Britain also flew small numbers of Flying Fortresses during the war. Germany captured and fixed up about 40 that crash-landed. They were mostly used for evaluation and interceptor training, but a few, flying German livery, also dropped agents and supplies in North Africa and the Middle East. There were rumors of captured B-17s disguised as Allied ones trying to mingle in with real Allied bomber streams and radio in their locations, but no solid evidence was ever found.

The Soviets didn't receive B-17s as Lend Lease, but got their hands on at least 73 which landed on the Eastern Front during shuttle bombing missions, and couldn't get in the air again due to damage or mechanical problems. Some of these were restored to flying condition, and later used in the project to build the Tupolev Tu-4, a copy of the B-29 Superfortress.

Neutral Switzerland confiscated one B-17 after it had to land. Japan rebuilt three damaged planes which still had their secret Norden bombsights, and used them for training and propaganda films. These were never found after the war.

Several Flying Fortresses were converted for special use during and after the war, often to serve as maritime patrol planes or air-sea rescue, dropping an airborne lifeboat to people in need.

Four were converted into cargo and V.I.P. carriers under the C-108 designation, the first being the personal plane of General Douglas MacArthur. At least 25 were redesignated as BQ-7 and turned into radio-controlled drones. These were used in Operation Aphrodite alongside similarly converted B-24s: they were packed with explosives, taken into the air by a pilot and a co-pilot who then parachuted out, then remotely flown to and into heavily fortified targets such as U-boat pens and V-weapon sites. Aphrodite was not very successful, as most targets were either taken out by conventional air attacks or captured by ground troops. Lieutenant Joseph P. Kennedy, the elder brother of future president John F. Kennedy, died on such a mission (albeit in a B-24) when the plane mysteriously exploded two minutes before his planned bailout.

The sturdy and distinctive aircraft quickly became a well-recognized symbol of American military and industrial might. A test model appeared on the silver screen as early as 1938, in the movie Test Pilot with Spencer Tracy and Clark Gable, the latter of whom actually flew on one as a gunner during the war. The B-17 continues to capture the imagination to this day, its most recent major media appearance being the TV show Masters of the Air. 45 Flying Fortresses are still in existence today, most of them in the United States, with fewer than 10 airworthy. Two planes, one of them in flying condition, can be seen on our Britain at War tour at Imperial War Museum Duxford.

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