: To maximize their defense, crews flew in staggered "combat box" formations, creating a "flying porcupine" of interlocking machine-gun fire that made individual attacks extremely dangerous for enemy pilots.

While synonymous with the European theater, the B-17 served globally:

: Early in the war, B-17s were used in the Battle of Midway and against Japanese shipping, though they were eventually replaced by the longer-range B-24 Liberator and B-29 Superfortress in that theater.

This strategy was tested during harrowing missions like "Black Thursday"—the second raid on the ball-bearing factories in Schweinfurt. Without long-range fighter escorts like the P-51 Mustang, B-17 formations faced devastating losses from German Luftwaffe interceptors. Legendary Durability

As highlighted in Martin W. Bowman’s classic work, Castles in the Air , the B-17 became the "main punch" for the during its daylight bombing offensive over Nazi Germany. Unlike the British Royal Air Force (RAF), which eventually shifted to night bombing, the Americans believed the B-17’s heavy defensive armament and the secret Norden bombsight allowed for high-altitude, precision daylight strikes.