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The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Competing against Douglas and Martin for a contract to build 200 bombers, the Boeing entry (prototype Model 299/XB-17) outperformed both competitors and exceeded the air corps' performance specifications. Although Boeing lost the contract (to the Douglas B-18 Bolo) because the prototype crashed, the air corps ordered 13 more B-17s for further evaluation. From its introduction in 1938, the B-17 Flying Fortress evolved through numerous design advances, becoming the third-most produced bomber of all time, behind the four-engined B-24 and the multirole, twin-engined Ju 88.
The B-17 was primarily employed by the USAAF in the daylight strategic bombing campaign of World War II against German industrial and military targets. The United States Eighth Air Force, based at many airfields in central and southern England, and the Fifteenth Air Force, based in Italy, complemented the RAF Bomber Command's nighttime area bombing in the Combined Bomber Offensive to help secure air superiority over the cities, factories and battlefields of Western Europe in preparation for the invasion of France in 1944. The B-17 also participated to a lesser extent in the War in the Pacific, early in World War II, where it conducted raids against Japanese shipping and airfields.
From its prewar inception, the USAAC (by June 1941, the USAAF) promoted the aircraft as a strategic weapon; it was a relatively fast, high-flying, long-range bomber with heavy defensive armament at the expense of bombload. It developed a reputation for toughness based upon stories and photos of badly damaged B-17s safely returning to base. The B-17 dropped more bombs than any other U.S. aircraft in World War II. Of the 1.5 million tonnes of bombs dropped on Nazi Germany and its occupied territories by U.S. aircraft, 640,000 tonnes were dropped from B-17s. In addition to its role as a bomber, the B-17 was also employed as a transport, antisubmarine aircraft, drone controller, and search-and-rescue aircraft.
As of May 2015, 10 aircraft remain airworthy, though none of them were ever flown in combat. Dozens more are in storage or on static display. The oldest of these is a D-series flown in combat in the Pacific and the Caribbean.
The Avro Lancaster is a British four-engined Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to the same specification, as well as the Short Stirling, all three aircraft being four-engined heavy bombers adopted by the Royal Air Force (RAF) during the same wartime era.
The Lancaster has its origins in the twin-engine Avro Manchester which had been developed during the late 1930s in response to the Air Ministry Specification P.13/36 for a capable medium bomber for "world-wide use". Originally developed as an evolution of the Manchester (which had proved troublesome in service and was retired in 1942), the Lancaster was designed by Roy Chadwick and powered by four Rolls-Royce Merlins and in one version, Bristol Hercules engines. It first saw service with RAF Bomber Command in 1942 and as the strategic bombing offensive over Europe gathered momentum, it was the main aircraft for the night-time bombing campaigns that followed. As increasing numbers of the type were produced, it became the principal heavy bomber used by the RAF, the RCAF and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing contemporaries such as the Halifax and Stirling.
A long, unobstructed bomb bay meant that the Lancaster could take the largest bombs used by the RAF, including the 4,000 lb (1,800 kg), 8,000 lb (3,600 kg) and 12,000 lb (5,400 kg) blockbusters, loads often supplemented with smaller bombs or incendiaries. The "Lanc", as it was known colloquially,[3] became one of the most heavily used of the Second World War night bombers, "delivering 608,612 long tons of bombs in 156,000 sorties". The versatility of the Lancaster was such that it was chosen to equip 617 Squadron and was modified to carry the Upkeep "Bouncing bomb" designed by Barnes Wallis for Operation Chastise, the attack on German Ruhr valley dams. Although the Lancaster was primarily a night bomber, it excelled in many other roles, including daylight precision bombing, for which some Lancasters were adapted to carry the 12,000 lb (5,400 kg) Tallboy and then the 22,000 lb (10,000 kg) Grand Slam earthquake bombs (also designed by Wallis). This was the largest payload of any bomber in the war.