B-17 Flying Fortress
On 28 July 1935 the Model 299 flew for the first time: just over three weeks later it was flown non-stop to Wright Field, Ohio, to be handed over for official test and evaluation. The 2,100-mile (3 380-km) flight had been made at an average speed of 252 mph (406 km/h), a most impressive performance which augured well for the future. The elation of the Boeing company was understandable, especially with confirmation that initial trials were progressing well. On 30 October 1935 hopes were dashed with the news that the prototype had crashed on take-off. Subsequent investigation was to prove that the attempt to take-off had been made with the controls locked, and in view of the satisfactory testing prior to this accident, the USAAC decided on the procurement of 13 YB-17s (later Y1B-17s), plus one example for static testing.
The prototype (X13372) which had crashed at Wright Field was powered by four 750 hp (559 kW) Pratt & Whitney R-1690-E Hornet radial engines. The cantilever monoplane wings were in a low-wing configuration, the wing section at the root so thick that it was equal to half the diameter of the circular-section fuselage; and wide-span trailing-edge flaps were provided to help reduce take-off and landing speeds. Landing gear was of the electrically retractable tailwheel type. Armament comprised five machine-guns, and a maximum bomb load of 4,800 lbs (2177 kg) could be carried in the fuselage bomb bay.
The initial Y1B-17 (36-149) flew for the first time on 2 December 1936, and differed from the prototype by having 930-hp (694-kW) Wright GR-1820-39 Cyclone radials, accommodation for a crew of nine, and minor changes in detail. Twelve were delivered between January and August 1937, equipping the USAAC’s 2nd Bombardment Group at Langley Field, Virginia. The thirteenth aircraft went to Wright Field for further tests and after one of the Y1B-17s survived without damage the turbulence of a violent storm, it was decided that the static test example would, instead, be completed as an operational aircraft. Designated Y1B-17A, this aircraft (37-369) was provided with 1,000 hp (746 kW) GR-1820-51 engines each fitted with a Moss/ General Electric turbocharger (supercharger powered by a turbine driven by exhaust gases). It flew for the first time on 29 April 1938, and subsequent testing by the USAAC gave convincing proof of the superiority of the turbocharged engine over those which were normally aspirated, and such engines were to become standard on all future versions of the Fortress.
The utilisation of the Y1B-17s, designated B-17 in service with the 2nd Bombardment Group, did little to improve relations between the US Army and US Navy. When three of the force were used to stage an ‘interception’ of the Italian liner Rex some 750 miles (1207 km) out in the Atlantic, to demonstrate that the USAAC was more than capable of defending the nation’s coastline, it sparked a row which dispersed the air power disciples from General Headquarters Air Force (GHQAF) to other commands, where they were remote from each other and potential influential supporters. Orders for additional B-17s had to be reduced after it had been underlined by Major General Stanley D. Embrick that … “the military superiority of a B-17 over the two or three smaller aircraft which could be procured with the same funds has yet to be established.” This helps explain why, despite the growing war clouds in Europe, the USAAC had less than 30 B-17s when Hitler’s forces invaded Poland on 1 September 1939.
The order for Y1B-17s was followed by a contract for 39 B-17Bs, more or less identical to the Y1B-17A prototype with turbocharged engines. The first of these flew on 27 June 1939, and all had been delivered by March 1940. In 1939 the B-17C was ordered, the first of the 38 on contract making its first flight on 21 July 1940. They differed by having 1,200 hp (895 kW) R-1820-65 engines, and by an increase from five to seven machine guns.
The B-17C was the first version of this bomber to be supplied to the RAF in Great Britain, which designated the 20 examples received in early 1941 as Fortress I. Equipping No. 90 Squadron, they were used operationally for the first time on 8 July 1941 when aircraft launched a high-altitude (30,000 ft / 9145 m) attack on Wilhelmshaven. In the 26 attacks made on German targets during the next two months the Fortress Is proved unsatisfactory, although there was American criticism of the way in which they had been deployed. Nonetheless, their use in daylight over German territory had proved that their operating altitude was an inadequate defence in itself, and so they needed more formidable defensive armament, for Messerschmitt Bf 109E and 109F fighters had little difficulty in intercepting them at heights of up to 32,000 ft (9750 m). Until improvements in the Fortress were made, or means found of deploying them more effectively, they were withdrawn from operations over Europe.
With the end of 1941 drawing near, the USA was soon to become involved in World War 11, initially in the Pacific theatre, but following the containment of the initial explosion of Japanese expansion it was decided that the Allies would first concentrate their efforts on bringing about a speedy conclusion of the war in Europe. Thus, large numbers of B-17s which otherwise would have found employment in the Far East were instead to equip the USAAF’s 5th Air Force in Britain. Those allocated to serve with the Anglo-American Northwest African Air Forces were later to become part of the US 15th Air Force.
In 1940 Boeing received an order for 42 B-17Ds. These differed little from the B-17C, but as a result of early reports of combat conditions in Europe were provided with self-sealing tanks and additional armour for protection of the crew, and these were delivered during 1941. The B-17E which followed was the first version to benefit from the RAF’s operational experience with its Fortress Is. A major redesign provided a much larger tail unit to improve stability at high altitude, and to overcome the criticism of inadequate defence 13 machine-guns were mounted in one manual and two power-operated turrets, radio compartment, waist stations and in the nose. Of the 512 of this version built under two contracts, the first flew on 5 September 1941. B-17Es were the first to serve with the 8th Air Force in Europe, with deliveries beginning in July 1942. They were used operationally for the first time by the 97th Bombardment Group, 12 aircraft being detailed for a daylight attack on Rouen on 17 August, with fighter escort provided by RAF Supermarine Spitfires.
The B-17F, of which the first flew on 30 May 1942, was the first version to be built in large numbers. Boeing produced 2,300 at Seattle, and further construction of 1,105 came from Douglas (605) and Lockheed Vega (500). Major changes included a redesigned nose, and strengthened landing gear to cater for a higher gross weight. Other changes included increased fuel capacity, the introduction of additional armour, provision of external bomb racks beneath the inner wings and, on late production aircraft, the introduction of R-1820-97 engines.
The B-17Es and B-17Fs became used extensively by the 8th Air Force in Europe, but in two major operations against German strategic targets, on 17 August and 14 October 1943, a total of 120 aircraft were lost. Clearly the Fortresses could not mount an adequate defence, no matter how cleverly devised was the box formation in which they flew. The hard truth was that without adequate long-range fighter escort they were very vulnerable to attack during mass daylight operations. Many of the losses were attributed to head-on attack, and the final major production version was planned to offset this shortcoming.
During late 1938, the U.S. Army Air Corps saw a need for additional heavy bombardment aircraft and approached Consolidated Aircraft to supplement B-17 Flying Fortress production by Boeing, Douglas, and Vega. When Consolidated president Reuben Fleet was approached, he stated that his company could build a better airplane. Consolidated began design of its Model 32 in January 1939.
By coincidence, Reuben Fleet had been approached by David R. Davis in 1937 to discuss wing-design theory. Not an aerodynamicist, Fleet insisted on having his chief engineer, Isaac Machlin “Mac” Laddon, and aerodynamicist George S. Schairer listen to the proposal. Extensive testing of the design in Cal Tech’s Guggenheim wind tunnel proved Davis’s concept to be far better than expected. The result was a high aspect- ratio wing that offered excellent long-range cruise characteristics. This wing that was applied to the design of the Model 32, which became the B-24 Liberator.
The B-24 was powered by four Pratt and Whitney R-1820 engines. It had an 8,800-pound bombload, a service ceiling of 28,000 feet, a cruising speed of 215 mph, and a range of 2,100 miles. Manned by a crew of 10, the B-24H thru B-24J models mounted 10 .50-caliber machine guns for defensive armament.
The B-24 was a stablemate of the B-17 in the European theater during World War II; however, its vulnerability to battle damage and dissimilar performance compared to the B-17 led Brigadier General Curtis E. LeMay, then commander of the 3d Air Division, to remove the Liberators completely in favor of B-17s. The result was that the 1st and 3d ADs were equipped with B-17s and the 2d AD with only B-24s.
The first raid on the Ploesti oil fields was flown by 13 B-24s from the Halverson Provisional Group on the night of 11/12 June 1942, marking the first Allied heavy bombardment mission against Fortress Europe. On 1 August 1943, the famed Ploesti raid was flown under Operation TIDAL WAVE with a force of 177 B-24s from five bomb groups (three of which were loaned from the Eighth Air Force in Europe).
In the Mediterranean theater of operations, B-24s far outnumbered B-17s. Of the 21 heavy bombardment groups in the Mediterranean late in the war, 15 were equipped with B-24s. The airplanes performed well on the long-range missions deep into Germany and Austria. B-24s did far better in the Pacific theater. The missions were long, over water, with no mountainous obstacles as were encountered in the European and Mediterranean theaters, and enemy resistance was not as intense.
B-24s were also modified for specialized roles as Ferrets, photoreconnaissance platforms, fuel tankers, clandestine operations, and radio/radar jamming.
The B-24 was built in greater numbers than any other U.S. combat aircraft. A total of 19,257 B-24s,RAF Liberators, C-87 transports, and Navy PB4Y-2 Privateers were built at two Consolidated plants as well as Douglas (Tulsa), North American (Fort Worth), and Ford (Detroit). Ford produced 6,792 complete aircraft and another 1,893 knockdown kits that were shipped by road to other plants for assembly and completion.
There is no question that the Boeing B-17 had better press-and a better name- than the Consolidated B-24. “Flying Fortress” evoked a vision of impregnability, while “Liberator” was much more abstract. The B-17 was indeed more of a fortress than was the B-24, but their respective crews defended their aircraft with passion-and in the case of the B-24, with a dash of derring-do attitude.
The B-17 was the older design, conceived by Boeing in 1934, with the first 13 planes delivered to what was then the Army Air Corps in 1938. Consolidated Aircraft Corporation-the 1923 successor to the Dayton-Wright Airplane Company-birthed the B-24 in 1939 as the next generation heavy bomber to supplant the Boeing XB-15, Douglas XB-19 and B-17.
The Lib was faster: 215 mph cruising speed for the B-24J, for example, versus 182 for the B- 17C. The Lib’s gracefully tapered 100-foot Davis airfoil wing (compared to the B-17’s 103-foot-span barn door of a wing) made the difference. The Lib had a larger bomb bay and a somewhat longer range. So it flew faster, farther and carried more bombs than the B-17. I trained on both the B-24 and the B-17 at the aerial gunnery school in Tyndall, Fla. Like my classmates, I fervently hoped to be assigned to B-17s. They were reputedly able to withstand punishment that would down a Lib. That reputation was substantiated by battle damage photos of B- 17s riddled by flak and fighter fire that had still managed to return to base. Not many photos of similarly damaged but surviving B-24s showed up. The Libs didn’t have that big low-aspect-ratio wing to sustain lift after serious aerodynamic damage. Also, enemy fighter pilots had discovered that a concentrated burst into the cross-feed fuel tines between the B-24’s shoulder high wing roots could be fatal.
On the liberator’s plus side, its tricycle landing gear made taxiing, takeoff and landing easier than the B-17’s conventional tailwheel configuration. The B-24 pilot’s seat was more comfortable too, with its six-way adjustments. A peculiar B-17 drawback was its parking brake control, accessible only to the co-pilot.
With some minor variants, the two bombers had comparable armament: nose turrets (beginning on the B-17 with the G model’s chin turret), top and ball turrets and waist window guns. The tail armament differed: a fully revolving power turret in the B-24, a less mobile turret in the B-17. The B-24’s ball turret retracted fully into the fuselage until it was lowered for action. The B-17’s ball turret rode about three-fourths permanently extended. For a belly landing, the gunner was helped out of his position, after which the ball was jettisoned.
In the event of ditching, there was no contest. That low B-17 wing could serve as a temporary pontoon while the crew scrambled into life rafts. The B-24’s high wing put the fuselage underwater- often badly damaged. Crew members, if they escaped at all, had to swim out.
The B-24, with its big slab-sided fuselage, said one contemporary pilot, “looked like a truck, hauled big loads like a truck and flew like a truck.” As a B-24 passed overhead in plain view, though, it was apparent that the fuselage was narrower, and that long, tapered wing lent the Liberator a deceptive gracefulness. Though more than 19,000 B- 24s were built-more than any other American wartime aircraft-the older, slower but tougher Fortress got the press glory.
In the final analysis, there is no real way to determine if either the B-24 or the B-17 was truly superior. But, the record of the two types indicates that, of the two, the Liberator design was more versatile and considerably more advanced than that of the Flying Fortress. The combat records of both types contradict the assertions that aircrews flying B-17s were “safer” than those in B-24s. The argument as to which was the best can never be settled. As long as there are still two surviving heavy- bomber veterans, one from each type, the B-17 veteran will believe his airplane was best, while the B-24 vet will know better.