The B-17 was the first Boeing military aircraft with a flight deck instead of an open cockpit and was armed with bombs and five .30-caliber machine guns mounted in clear "blisters." The first B-17s saw combat in 1941, when the British Royal Air Force took delivery of several B-17s for high-altitude missions. As World War II intensified, the bombers needed additional armament and armor. The B-17E, the first mass-produced model Flying Fortress, carried nine machine guns and a 4,000-pound bomb load. It was several tons heavier than the prototypes and bristled with armament. It was the first Boeing airplane with the distinctive — and enormous — tail for improved control and stability during high-altitude bombing. Each version was more heavily armed. In the Pacific, the planes earned a deadly reputation with the Japanese, who dubbed them "four-engine fighters." The Fortresses were also legendary for their ability to stay in the air after taking brutal poundings. They sometimes limped back to their bases with large chunks of the fuselage shot off.
Only a few B-17s survive today; most were scrapped at the end of the war. Some of the last Flying Fortresses met their end as target drones in the 1960s — destroyed by Boeing "Bomarc" missiles.