B-17D

The Royal Air Force's experiences with the B-17C, which was concurrently entering service with the USAAC, highlighted several serious deficiencies in the aircraft as a combat platform. Issues such as the formation of telltale condensation trails at altitude, inaccurate bombing due to difficulties with the Sperry bombsight, and inadequate bomb load proved challenging to resolve.

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However, Boeing and the Air Corps did implement changes to the "Fortress" bombers still in production. Solutions were in the works to address problems like lateral instability and rearward defense, with the impending arrival of the improved B-17E model.

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Specifically, the Army specified 32 modifications for the second batch of B-17Cs, which were so extensive that the updated aircraft were redesignated as B-17Ds. While the only obvious external change was the addition of cowling flaps for better engine cooling, the internal upgrades were substantial. These included bladder-type fuel tanks, armor plating, a 24-volt electrical system, revised bomb racks, and the removal of lower windows for oblique photography. Most significantly, the armament was doubled in the ventral and dorsal gun positions, and additional mounts were added for the nose gun.

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The new B-17Ds emerged in a natural metal finish, while B-17Cs returned for modification were painted in the Army's new olive drab over neutral gray scheme. Though the modified Cs received all the internal changes specified for the D model, they lacked the distinctive cowl flaps, making the two versions nearly indistinguishable.

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Cowl Fllaps for the 'D'

The B-17D's increased payloads and high-altitude operations placed immense thermal demands on the engines. In an effort to enhance cooling, Boeing fitted the engine cowlings with trailing-edge flaps - the sole major external difference between the B-17C and B-17D models.

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While most B-17Cs and many B-17Bs underwent modification to incorporate many of the 'D' model's internal upgrades, these changes did not always include the distinctive cowling flaps. The B-17D featured a host of other enhancements as well, including revised electrical, fuel, and oxygen systems, additional armor plating, improved bomb racks, and self-sealing fuel tanks - the earlier tanks having proven prone to leaks.

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These comprehensive upgrades addressed critical shortcomings of the original B-17 design, equipping the bomber to operate effectively at the high altitudes and heavy weights required for strategic bombing. The cowling flaps, while a seemingly minor change, were an essential component in managing the intense thermal loads generated by the B-17D's powerful engines under such demanding conditions.

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A B-17D warming up its engines, with cowling flaps clearly visible

 

Costs put the Bomber Programme Under Threat

During 1939-1940, the very future of the Boeing B-17 program hung in the balance. In 1939, Boeing found itself losing money on the aircraft and proposed increasing the per-unit price to $205,000. However, the Air Corps refused to accept this, insisting they would pay no more than $198,000 "and not a dime more."

Even with World War II raging in Europe, there was no compromise to be found between Boeing and the Army Air Corps. The newly appointed Chief of the Air Corps, General H.H. "Hap" Arnold, made his best efforts to negotiate a price settlement, but to no avail. Despite the B-17C model already being under construction, it appeared that without a financial solution, production of the Flying Fortress would be abandoned altogether.

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This impasse threatened to derail the entire B-17 program at a critical juncture, just as the aircraft's importance was becoming increasingly evident amid the escalating global conflict. The Air Corps' steadfast refusal to budge on the price, coupled with Boeing's mounting financial losses, created a high-stakes standoff that called into question the very future of this pivotal bomber design. Resolving this contractual stalemate would prove essential to ensuring the B-17's continued development and its eventual emergence as a decisive weapon in the Allied air war.

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With the Boeing B-17 program on the brink of collapse, a final negotiation meeting was convened, which Boeing had already considered a lost cause. Recognizing the stakes, General Carl Spaatz was dispatched by Air Corps Chief "Hap" Arnold to represent their interests.

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Spaatz knew he had to find a resolution, or the entire heavy bomber program would be abandoned. Employing a savvy tactic, he suggested they explore what features could be removed from the aircraft to reduce the price. This pragmatic approach proved successful, and a compromise rock-bottom price of $202,500 per B-17 was ultimately agreed upon.

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This hard-fought deal salvaged the viability of the Flying Fortress, paving the way for the contracted production of the improved B-17D model. Spaatz's willingness to consider creative solutions, rather than simply holding the line, allowed this pivotal bomber design to survive the impasse and go on to become a decisive Allied weapon.

 

 

 

 

 

 

 

 

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A B-17D in flight over the ocean

 

Not Quite there with Powered Turrets

As part of the B-17D's comprehensive upgrade, Boeing had planned to incorporate power-operated turrets produced by Sperry on late-production models. However, development delays hampered the turrets' timely delivery, and only a single experimental installation was completed. This lone turret was positioned just aft of the cockpit, replacing the gunnery controller's Plexiglas dome found on earlier B-17C and D variants.

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Despite the setback with the Sperry turrets, the majority of B-17D bombers were still delivered to the Air Corps during the early spring of 1941. Most were immediately dispatched to reinforce the 5th Bomb Group in Hawaii, while others were used to re-equip the 19th Bomb Group, which had relocated from the United States to the Philippine Islands later that year.

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While the power-operated turrets failed to materialize as planned, the B-17D still represented a significant leap forward in capability compared to previous models. Its robust defensive armament, enhanced systems, and improved aerodynamics made it an increasingly formidable strategic bomber. The urgency with which these aircraft were deployed to critical Pacific theaters underscores the U.S. military's pressing need for such advanced and capable aerial assets.

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Forts Fight in the Pacific

When the Japanese attacked Pearl Harbor in December 1941, the U.S. Army Air Force possessed 150 B-17 "Flying Fortresses" globally, with a third of them deployed across the Southwest Pacific. In Hawaii, the defense force included 12 B-17C/D models among a total of 131 military aircraft. Meanwhile, the U.S. protectorate of the Philippine Islands hosted 176 warplanes, comprising 29 B-17Ds and 6 B-17Cs organized into four squadrons - one assigned to the 7th Bombardment Group, and three to the 19th Bombardment Group, all under the latter's command. One 7th Group squadron, along with a fourth for the 19th, were in the process of deploying to the Philippines via Hawaii when the Japanese assault occurred.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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A 19th BG  B-17D 'bombing up' in the Pacific Theatre

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In the devastating attack on Pearl Harbor, four B-17Ds and a solitary B-17C were destroyed. Across the Philippines, fourteen of the 19th Group's B-17s were wrecked at their Luzon airbase. Over the next two weeks, another seven were lost in brave but largely futile attempts to strike back at the invading Japanese forces and naval assets. By month's end, Philippine bases had become untenable, and the remnants of the 19th Group withdrew nearly 2,000 miles south to Darwin, Australia - only to be pushed 1,500 miles northwest to Java for further action. Of the B-17s that reached Australia, only ten remained fit for continued operations. Yet with Japanese landings in Borneo and other points to the south, these long-range "Flying Fortresses" were desperately needed, as they represented the only assets capable of reaching these widely scattered locations.

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The devastating losses suffered by America's B-17 force in the Pacific in those critical early weeks of the war underscored the pivotal role these bombers would play in the looming air campaign. Despite the heavy blows, the surviving aircraft's unique capabilities ensured their continued, essential employment across the far-flung battle space.

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