Boeing B-17 Flying Fortress

In May 1934, the United States Army Air Corps released a specification for a multi-engined bomber that could carry 2,000lb bombs over a distance of 1,020 – 2,200 miles, at a speed of 200 – 250 mph. A deadline of August 1935 was set for a prototype to be ready for testing. Boeing submitted their Model 299, which they had started designing in June 1934, and would be powered by four engines and normally have a crew of ten, consisting of pilot, co-pilot, navigator, bomb-aimer, flight engineer, wireless operator, two waist gunners, ball turret gunner and rear gunner.

On the 16th July 1935, at Boeing Field, the aircraft was introduced to the press, with the headlines the next day proclaiming a '15-ton Flying Fortress', leading to Boeing registering it as the Model 299 name. Twelve days later, on the 28th July 1935, the Model 299, powered by four 750-hp Pratt & Whitney R-1690 Hornet engines, made its first flight, before being flown to Wright Field for testing and evaluation a few weeks later. However, during testing a setback occurred on the 30th October 1935, when the prototype crashed on take-off, the investigation was to conclude that the controls were locked when take-off was attempted.

Despite this setback, the United States Army Air Corps ordered thirteen YB-17s, redesignated Y1B-17 later on, as a result of the successful testing before the accident. The 2nd December 1936 saw the first Y1B17 fly, featuring a change in engines, the aircraft was now powered by the 930-hp Wright GR-1820-39 Cyclone engine. The United States Army Air Corps 2nd Bombardment Group, based at Langley Field, received twelve aircraft during the first eight months of 1937, with the remaining aircraft undergoing more testing at Wright Field. A fourteenth aircraft that had been ordered for static tests would become the Y1B-17A, later the sole B-17A, and this made its maiden flight on the 29th April 1938.

The B-17B followed, with the first example flying on the 27th June 1939. Powered by the 1,200-hp Wright R-1820-51 engine, thirty nine were built, however, they would only serve in the training, transport, liaison and messenger roles and were redesignated to RB-17B in October 1940.

The B-17C, also known as the Fortress Mk I, flew for the first time on the 21st July 1940. Powered by the 1,200-hp Wright R-1820-65 engine, its top speed was 323 mph, range 3,400 miles with a service ceiling of 37,000 ft. Armament was six 0.50-in machine-guns and one 0.30-in machine-gun, bomb load was 4,800lb. This was the first variant to enter combat during the Second World War (1939 – 1945). This was with the Royal Air Force, when No. 90 Squadron, which had been reformed on the 7th May 1941 at RAF Watton, received their first examples that same month.

Two months later, on the 8th July 1941, No. 90 Squadron used the aircraft for its first combat sortie, when three took part in a Bomber Command raid against Wilhelmshaven, Germany. The Fortress Mk I would take part in a further twenty six raids on Germany over the next two months, losing three aircraft on operations. The Fortress Mk I was deemed unsatisfactory by Bomber Command and the remaining aircraft were transferred to Coastal Command.

The B-17D, which flew for the first time on the 3rd February 1941, featured additional armour and self-sealing fuel tanks, and was powered by the 1,200-hp Wright R-1820-65 engine, giving the aircraft a top speed of 323 mph, a range of 3,400 miles and a service ceiling of 37,000 ft. Armament consisted of six 0.50-in machine-guns and one 0.30-in machine-gun, with a bomb load of 4,800lb.

The next variant was the B-17E, also known as the Fortress Mk IIA, which flew for the first time on the 5th September 1941. Powered by the 1,200-hp Wright R-1820-65 engine, its top speed was 317 mph, range 3,200 miles with a service ceiling of 36,000 ft. Armament was eight 0.50-in machine-guns and one 0.30-in machine-gun, bomb load was 4,200lb. Three months later, the United States was drawn into the Second World War after the Japanese attack on Pearl Harbor on the 7th December 1941. It would be the B-17E that was the first of the type used by the Eighth Air Force for operations over Europe, when on the 17th August 1942, twelve aircraft from the 97th Bombardment Group, escorted by Supermarine Spitfires of the Royal Air Force, attacked the marshalling yards in Rouen, France. Only two aircraft sustained minor damage.

Flying for the first time on the 30th May 1942, the B-17F, also known as the Fortress Mk II, featured a redesigned nose and more armour. It was powered by the 1,200-hp Wright R-1820-97 engine, this gave the aircraft a top speed of 325 mph, a range of 2,800 miles and a service ceiling of 37,500 ft. Armament consisted of eleven 0.50-in machine-guns, with a bomb load of 8,000lb. Along with the B-17E, it would be the variant that the Eighth Air Force would use the most, however, mounting losses during daylight raids were to show that the aircraft, either on its own or flying in formation, could not defend itself, with a particular vulnerability to head-on attacks.

The final variant was the B-17G, also known as the Fortress Mk III, and this featured a gun turret in the nose section to help protect the aircraft during head-on attacks. Powered by the 1,200-hp Wright R-1820-97 engine, its top speed was 302 mph, range 3,400 miles with a service ceiling of 35,600 ft. Armament was thirteen 0.50-in machine-guns, bomb load was 8,000lb. Despite the new nose turret, daylight raids into Germany saw heavy losses, and it wasn't until the introduction of escort fighters equipped with external fuel tanks that losses began to be reduced.

The B-17 was used wherever US forces were, in the Pacific, they were used for close-support bombing, patrol and reconnaissance. It wouldn't be until August 1959 that the United States Air Force retired their last B-17s.

In total, 12,731 aircraft were built.