Flying Fortress

The "B-17", a.k.a. the "Flying Fortress" is a four-engine heavy bomber aircraft developed for the United States Army Air Corps. The USAAC touted the aircraft as a strategic weapon; it was a potent, high-flying, long-ranging bomber capable of unleashing great destruction, able to defend itself, and having the ability to return home despite extensive battle damage. This very low droning sound of the Flying Fortress usually means bad news for those on the ground.