In the years since 1959, Andrews' flight operations and importance have increased greatly. In 1961, the last of the Military Air Transport Service's flying units at Washington National Airport transferred to Andrews. This was followed a year later by the transfer to Andrews of all fixed-wing flying activities from Bolling Air Force Base. Andrews has become firmly established as the main port of entry for foreign military and government officials en route to Washington and the United States. In July 1961, the official presidential aircraft was stationed here, known as "Air Force One" when the president is on board. Before 1961, the presidential airplane had been kept at Washington National Airport and Bolling AFB.