During World War II the military airfield served as a refueling and transit depot. During the Cold War, Naval Air Station Keflavik played an important role in monitoring marine and submarine traffic from the Norwegian and Greenland seas into the Atlantic Ocean. Forces from the United States Air Force were added to provide radar monitoring, fighter intercept, in-flight refueling, and aerial/marine rescue. After the collapse of the Soviet Union, however, the base's role was cast into doubt. The base officially closed on 30 September 2006, when the United States withdrew the remaining 30 military personnel.