tail gunner

Wiktionary

1. n. One who operates the gun or guns in in the tail of a military aircraft, usually a bomber.
2. n. colloquial One whose function in an organization is to defend it from attackers, for example, in public relations or public affairs.

GNU Webster's 1913

1. n. (Mil.) A member of the crew of a bomber airplane who operates the defensive gun at the rear of the airplane.