Boeing B-17 Flying Fortress

The Flying Fortress was conceived in the mid-1930s around a uniquely American idea: that a heavily armed bomber, flying high and in tight formation, could defend itself in daylight without fighter escort and bomb with pinpoint precision. Boeing gambled its own money on a four-engined design when the Air Corps had asked only for a twin, and the prototype Model 299 first flew on 28 July 1935.

A journalist who saw the bristling array of defensive guns dubbed it the 'Flying Fortress', and the name stuck. The gamble nearly ended in disaster when the prototype crashed on a test flight, but the Air Corps had seen enough to order it into development. The doctrine it embodied — the self-defending daylight bomber — would be tested to destruction over the skies of Europe.

Combat experience drove a relentless evolution. Early models proved too lightly armed, and successive versions piled on guns, armour and self-sealing tanks until the bomber bristled with up to thirteen .50-calibre machine guns. The greatest vulnerability — the head-on attack, against which the nose was nearly defenceless — was finally answered by a powered chin turret.

That fix defined the ultimate model, the B-17G, which became the standard heavy bomber of the Eighth Air Force and was built in greater numbers than all earlier marks combined. Stable, strong and able to fly and bomb from above 7,500 m, the Fortress was never the fastest or longest-ranged heavy bomber of the war — the B-24 carried more, further — but it was the steadiest gun platform and the one crews trusted most to bring them home.

Some 12,700 Fortresses were built across all versions, the overwhelming majority being the definitive B-17G. Beyond the bomber role the airframe was adapted to many specialised tasks: long-range air-sea rescue, photographic reconnaissance, and electronic-warfare and radio-countermeasures work against German defences.

The most heavily modified were the YB-40 gunship — a Fortress turned into a flying arsenal to escort other bombers, which proved too heavy to keep formation — and a handful of war-weary aircraft packed with explosives as radio-controlled flying bombs. After the war Fortresses served on as transports, drones and even airliners, and a few flew for foreign air forces into the 1950s.

Crews of the Eighth Air Force flew the Fortress through the bloodiest air battles of the European war. Unescorted deep-penetration raids on targets like Schweinfurt and Regensburg in 1943 were savaged by German fighters, and for a time the loss rate threatened to break the whole daylight-bombing strategy. These were among the most costly air operations the United States ever mounted.

The arrival of the long-range P-51 Mustang changed everything. With escorts able to accompany them all the way to Berlin and back, from 1944 the Fortresses ranged over Germany almost at will, pounding its industry and cities by day while the RAF bombed by night. Tales of B-17s limping home with engines dead, tails shattered and crews wounded gave the type its almost mythical reputation for survivability.

The price of the daylight doctrine was paid in 1943. Over Schweinfurt and Regensburg on 17 August 1943 the Eighth Air Force lost 60 of 376 attacking bombers in a single day; on the second Schweinfurt raid — “Black Thursday”, 14 October 1943 — 77 more Fortresses were destroyed or written off out of 291 dispatched. Unescorted deep penetration was, for two months, simply suspended.

In all, the Eighth Air Force lost around 4,750 B-17s on combat operations, and its casualty roll — some 26,000 dead — exceeded that of the entire US Marine Corps in the war. Against that stood the morale of crews who finished: when Memphis Belle completed her 25-mission tour in May 1943, the crew toured America as living proof that the odds could be beaten.

The Boeing B-17 Flying Fortress became the enduring symbol of the American daylight bombing campaign over Europe. Tough, stable and beloved by the ten-man crews who took it to war, it dropped more bombs on Nazi Germany than any other American aircraft and absorbed punishment that would have destroyed lesser machines.

Its story is also the story of a doctrine paid for in blood — the belief in the self-defending bomber, which proved tragically costly until the escort fighter arrived to make it work. Yet for all that, the Fortress endures in memory as the aircraft that, more than any other, carried the war into the heart of Germany and brought its young crews back across the North Sea.

• Donald L. Miller, Masters of the Air (Simon & Schuster, 2006) — the American bomber war.
• Roger A. Freeman, B-17 Flying Fortress and The Mighty Eighth (Arms & Armour / Cassell).
• Martin W. Bowman, B-17 Flying Fortress Units of the Eighth Air Force (Osprey).
• Edward Jablonski, Flying Fortress (Doubleday).