The United States Air Force organizes, trains, equips, and supports combat forces for unified and specified combatant commands through ten major commands headquartered at bases across the United States and overseas, including Air Combat Command at Langley Air Force Base, Virginia; Air Force Global Strike Command at Barksdale Air Force Base, Louisiana; and U.S. Air Forces in Europe at Ramstein Air Base, Germany. It structures operations via numbered air forces, wings, groups, squadrons, and flights, with the wing as the basic unit handling composite or single aircraft types. Current senior leaders include Dr. Troy E. Meink as the 27th Secretary of the Air Force, General Kenneth S. Wilsbach as Chief of Staff, General John D. Lamontagne as Vice Chief of Staff, Matthew L. Lohmeier as the 29th Under Secretary, and Chief Master Sgt. David R. Wolfe as the 21st Chief Master Sgt. of the Air Force. Established as a separate service effective September 18, 1947, under the National Security Act, with W. Stuart Symington as first Secretary and Gen. Carl A. Spaatz as first Chief of Staff. Headquarters is located at the Pentagon in Arlington, Virginia.