B-17E
By the end of 1941, Boeing had developed a visually striking new model of the B-17 bomber that incorporated crucial lessons from combat operations. Designated the B-17E, this aircraft entered service with the US Army Air Force that December.
The most notable change was the much larger tail assembly, which featured an imposing dorsal fin and expansive horizontal stabilizer. This enhanced the B-17E's control and stability at high altitudes, a critical improvement for its bombing role.
Furthermore, this visual change would clearly divide the early and late Flying Fortresses - all Forts after this model were defined by this large and distinctive tail. USAAF personnel affectionately referred to them as "Big Ass Birds".
The B-17E represented the most radical transformation of the Flying Fortress design to date. Intended to directly succeed the B-17D, the new model featured a completely overhauled rear fuselage and tail assembly. The most striking visual feature of the B-17E was its enlarged vertical fin, which was derived from the design of Boeing's Model 307 Stratoliner commercial airliner.
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The Stratoliner had been developed concurrently with the B-17, sharing the same basic wing and powerplant architecture. By adapting the airliner's distinctive tail design for the new bomber variant, Boeing was able to carry over proven aerodynamic characteristics that enhanced the B-17E's performance and stability.
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Boeing Model 307 Stratoliner - inspiration for the B-17E tail design
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This seamless integration of proven design elements from the commercial Stratoliner allowed Boeing to rapidly develop an even more capable military derivative in the form of the B-17E. The resulting large, imposing vertical fin became an instantly recognizable hallmark of the updated "Flying Fortress" - a visual cue that signaled the aircraft's enhanced flight qualities compared to earlier B-17 models.
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The B-17E's extensive changes were immediately apparent. The entire fuselage aft of the radio room was redesigned, becoming larger and straighter. Weight increases necessitated enlarging the horizontal stabilizer from 33 feet, 9 inches to 43 feet.
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A key driver behind the B-17E's radical redesign was the requirement for an effective tail gun position. Importantly, Boeing opted against installing one of the new power-operated turrets in this location. The bulky size of one of these powered turrets would have necessitated further enlarging the rear fuselage diameter or adding an unsightly bulge behind the tail. To avoid these compromises, which would have increased aerodynamic drag, Boeing instead favored maintaining the B-17's sleek, tapering aft fuselage.
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Therefore the rear fuselage was extended by nearly 6 feet and incorporated a compact gunner's compartment at the extreme rear, where a crewman could hand-operate a pair of 0.50-inch (12.7mm) machine guns while seated in a kneeling position.
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Profile view of a B-17E showing the new tail, tail gun position and remotely operated ventral turret
Though forgoing the power turret may have seemed like a missed opportunity, Boeing's decision demonstrated an adept balance of operational requirements and engineering constraints. By prioritizing the aircraft's aerodynamic efficiency, they ensured the B-17E retained the high-altitude performance essential for its strategic bombing role. This careful optimization of form and function made the new model an even more formidable and capable successor to earlier Flying Fortress variants.
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The aircraft's other gun positions also underwent a comprehensive overhaul. Most notably, the 'E' model featured a power-operated top turret mounted just aft of the flight deck, which was equipped with two 0.50-inch machine guns and a Sperry computing sight.
Additionally, early B-17Es were fitted with a remotely-controlled Sperry belly turret, located in the fuselage aft of the radio room. This ventral turret was equipped with two 0.50-inch machine guns which were aimed via a periscope sighting system. Ultimately this configuration gave inadequate field of vision and was not considered effective at targeting fast moving fighters.
To address this shortcoming, the remotely sighted Sperry belly turret was replaced with a manned Sperry ball power turret, also armed with two 0.50-inch machine guns. This modified turret was first introduced on the 113th B-17E, serial number 41-2505.
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Closeup of the remotely operated Sperry Turret. The sighting station can be seen to the right of it
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These enhancements to the B-17E's defensive armament, especially the more capable powered turrets, were important upgrades that significantly improved the aircraft's ability to defend itself against enemy fighters during high-altitude bombing missions.
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Increased Weight and Lower Performance, but the B-17 Comes of Age
As the B-17E's armored protection and equipment were enhanced, the aircraft's gross weight climbed to 54,000 pounds (24,494 kg). This substantial increase in mass inevitably resulted in a drop in cruising speed, from 231 mph (372 km/h) down to just 210 mph (338 km/h).
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Despite these performance tradeoffs, the B-17E represented the first model of the "Flying Fortress" to enter large-scale production. By the time deliveries were completed, a total of 512 B-17Es had been built, including 45 that were sent to the Royal Air Force and designated the Fortress Mk IIAS.
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While the B-17E's enhanced defensive systems and increased payload capacity came at the cost of lower top speed, this was an acceptable compromise that transformed the aircraft into a more resilient and capable strategic bomber.
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Production is Ramped Up
Despite the B-17's obvious capabilities, the Materiel Division's trademark dithering and cost deliberations delayed Boeing from securing a contract until August 1940. When it finally came, it was for a substantial order of 277 aircraft.
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Just over two weeks later, this initial contract was expanded by an additional 235 planes, bringing the total to 512 B-17Es. In light of the radical redesign, a new Army designation would have been justified. However, Boeing distinguished the model as the 299-O, while the Army opted to retain the B-17 designation, labeling it the 'E' variant.
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Colour view of two B-17Es in flight. The machine nearest the camera was destined for the RAF until requisitioned.
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The onset of World War II and the United States' own rearmament program led to significant production delays during 1940-41, as the aviation industry struggled with shortages of raw materials and components. As a result, the first B-17E was delivered a full 150 days behind schedule.
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Yet, in the wake of the Japanese attack on Pearl Harbor and Germany's declaration of war, America's industrial juggernaut rapidly mobilized. With diminished bottlenecks and improved manufacturing efficiency, the final 512th B-17E was delivered nearly 50 days ahead of the revised timeline, in late May 1942.
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This remarkable turnaround, transforming chronic delays into accelerated production, underscored the American industrial base's vast potential when unshackled and directed towards the war effort. It paved the way for the B-17 to become a dominant force in the Allied strategic bombing campaign.
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The BVD
As the prospect of war loomed, the order book situation for the B-17 underwent a dramatic transformation. Where finance had previously been a major obstacle, it was no longer a constraint, and the Army Air Corps now demanded as many B-17s as Boeing could produce.
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With Boeing's production capacity fully committed, the U.S. government sought to expand the bomber's manufacturing base. They successfully persuaded Lockheed Vega and Douglas to license-build the B-17E model as well.
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To coordinate these multi-company activities, a centralized committee was established in May 1941, which became known as the "BVD" - the initials of the three participating manufacturers: Boeing, Vega, and Douglas.
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Though the BVD was formed at a time when the B-17E was the primary model, Boeing was already working on a successor; so it was the subsequent B-17F that was produced by the BVD and in huge numbers.
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Nonetheless, the B-17E remains notable as the first of the Big Tailed Forts - emblematic of the iconic airframe familiar to enthusiasts.
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