As the storm of World War II shook the world, Boeing-designed B-17 bomber fleets darkened European skies, dropping 640,036 bombs on designated targets. Described by General H. H. “Hap” Arnold, as the “backbone of our worldwide aerial offensive,” the B-17 Flying Fortress served in every World War II combat zone. Boeing, Douglas, and Lockheed Vega produced 12,731 B-17s at plants across the country, and the four-engine bombers became legendary for their ability to stay in the air after taking brutal poundings.