The Thirteenth Air Force (13 AF) was a numbered air force of the United States Air Force Pacific Air Forces (PACAF). It was last headquartered at Hickam Air Force Base on the island of Oahu, Hawaii. 13 AF has never been stationed in the continental United States. It was one of the oldest continuously-active numbered air forces in the United States Air Force. Returning to the Philippines after the Vietnam War ended in 1975, the command remained there until the 1991 evacuation of Clark Air Base after the Mount Pinatubo eruption and the United States withdrawal of military forces afterward.