Boeing plants built a total of 6,981 B-17s in various models, and another 5,745 were built under a nationwide collaborative effort by Douglas and Lockheed (Vega). An estimated 4,750 of these aircraft were lost in combat. The Fortresses were 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 and control surfaces shot away.