The Boeing B-17 Flying Fortress is a four-engine 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 outperformed both competitors and exceeded the air corps' performance specifications. Although Boeing lost the contract 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. The B-17 was primarily employed by the United States Army Air Forces (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.

Info: B-17 Flying Fortress 323rd BS, 91st BG "Nine-O-Nine" RAF Bassingbourn, England, 1944 - Smithsonian Series