Inspector General, a military officer who inquires into and reports on all matters affecting efficiency, economy, and discipline within his branch of the armed forces. The U.S. Army, Navy, Marine Corps, and Air Force each has an inspector general who reports to the secretary and chief of staff of his branch. Members of each IG's staff are assigned to major units. The inspector general of the Air Force has additional powers, including the direction of air force security policy and the counterintelligence program.