17

In 1934, the US Army decided it was time for a newer 4-engine bomber. Boeing then developed the B-17 which, was so well-armed and tough, it quickly earned the nickname "The Flying Fortress." The Fortresses were legendary for their ability to stay in the air after taking brutal poundings, but could also dish it out. The B-17E had an armament of nine machine guns and a 4,000 pound normal bomb load.