Senior Airman William Knight sends Rex through a tunnel during obedience training. U.S. Air Force Senior Airman William Knight, a dog handler, sends Rex, a military working dog, through a tunnel during obedience training at Ellsworth Air Force Base, S.D., on May 7, 2009. Knight and Rex are assigned to the 28th Security Forces Squadron. SHARE: Download: Full Size (0.04 MB) Credit: VIRIN: 939561-Z-YMX80-745.jpg Photo Gallery