The B-17 was designed in 1934 by Boeing to take part in a US Army Air Corps competition to produce a modern multi-engined bomber. Their Model 299 prototype first flew on 28 July 1935, and a Journalist nicknamed it the ‘Flying Fortress’.
In October 1935, the prototype crashed and the design lost out to the Douglas DB-1. Fortunately, the Air Corps recognized it was a promising aircraft and ordered 13299s in January 1936, which they designated the Y1B-17. Not long after, the Y1B-17 became the B-17, and Wright Cyclone engines replaced the 299’s Pratt 8 Whitney Hornet engines.
In 1938, another big advance was the introduction of turbo super-chargers to the engines of a B-17A test aircraft that could take it to an altitude of 9,144 metres (30,000 feet). The B-17B became the first production model, but at the outbreak of World War II, only 30 of them were operational. In 1940,38 B-17CS were built with better-armoured protection, and only 42 B-17DS were rolled out before mass production of the redesigned B-17E, B-17F and the ultimate B-17G models. Out of the total production run of 12,725 B-17S, 512 were E-class, 3,400 were F-class and 8,680 were G-class.
To fulfil its promise as a precision strategic bomber, it was fitted with the top-secret Norden bombsight. This was a gyroscope-stabilised device that calculated the dropping angle and drift of the aircraft to enable accurate high-altitude bombing.
It is believed around 5,000 B-17S were shot down or destroyed in their mission to eliminate industrial and military targets during WWII.
The B-17 went through a range of modifications and design changes in line with experience and mission requirements. Its range could be extended with the use of bomb bay and ‘Tokyo’ fuel tanks, and it could carry additional bombs on special external racks. Defensive weaponry on the craft was revised and changed on various models, with the introduction of powered turrets and additional gun slots. The weight of the ammunition meant that each gunner got about 500 rounds that would give one minute of constant fire. Despite being a ‘flying fortress’ it did need nippier fighter aircraft escorts to give it the best protection during daylight raids.
The US 8th Air Force began using B-17ES in daylight raids on Nazi-occupied Germany. The extra visibility afforded by daylight allowed for precise bombing of the targets and promised to be more successful in the long run than night-time raids.
Their first attack on Germany occurred on 27 January 1943, which consisted of a force of 91B-17S and B-24S. It was found that the B-17S could protect themselves from cross-fire and attacking fighters by flying in wedge-shaped formations, but they were very vulnerable to head-on attacks.
A year later, the improved B-17G carried chin turret machine guns that could deal with frontal attacks. Instead of flying in wedges of 18 aircraft, they now flew in a formation of three wedges, one on top of the other, that consisted of 12 aircraft in each wedge. Although this offered more protection from enemy attack, it meant that collisions between the tightly packed aircraft were more common.
The B-17 was originally conceived as a coastal defence weapon or strategic day bomber, so when the RAF was supplied with 20 B-17CS in 1941 they were unimpressed by its inability to bomb accurately above 6,096 metres (20,000 feet) -these were not fitted with the Norden bombsight – and its lack of armoured protection. 90 Squadron used the aircraft in the Middle East and for reconnaissance missions by Coastal Command.
The vast majority of B-17S were used by the US 8th Air Force to fight the war in Europe. Some B-17S were deployed in the Far East and South Pacific where they were involved in bombing Japanese convoys and troop concentrations in Java and the Philippines. In the Mediterranean and North Africa, B-17S attacked naval targets and took part i: night-time reconnaissance missions.
After the war, B-17S were modified by civilian airlines to carry passengers or cargo, or to fight forest fires or carry out photographic surveys. The Israeli Air Force used a small number in the 1948 War of Independence and the US Army Air Force used them for testing equipment, target drones and weather reconnaissance.