U.S. Air Force TECH. SGT. Randall Stone, from the 142nd Fighter Wing, Oregon Air National Guard, opens a valve on a liquid oxygen tank during exercise William Tell 2004 at Tyndall Air Force Base, Fla., on Nov. 9, 2004. This is the 50th Anniversary of the William Tell competition, an exercise that tests an aircrew's ability to perform under combat conditions. (USAF PHOTO by MASTER SGT. Robert W. Valenca) (Released)