One of the unique features of the B-17 bomber was the ball turret. Made of Plexiglas and about four feet in diameter, the ball turret was a sphere attached to the bottom of the airplane. Armed with two .50-caliber machine guns and capable of rotating 360 degrees, the ball turret's gunner was responsible for protecting the otherwise-exposed underbelly of the flying fortress. By all accounts, the ball was very small and very cramped.