The United States Eighth Air Force, based at many airfields in central, eastern and southern England, and the Fifteenth Air Force, based in Italy, complemented the RAF Bomber Command's night-time 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 was primarily employed by the USAAF in the daylight strategic bombing campaign of World War II against German industrial, military and civilian targets. 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 Consolidated B-24 Liberator and the multirole, twin-engined Junkers Ju 88.

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. 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. The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC).

Betty bomber crew positions