PEASE AIR NATIONAL GUARD BASE, N.H. -- U.S. Air Force Senior Airman Stephen Drown, front, and Senior Airman Riley Burley, 157th Security Forces Squadron, N.H. Air National Guard, enter a building during an active shooter training exercise at Pease Air National Guard Base April 5, 2014. The previously scheduled training comes just days after a gunman killed three people and injured 16 at Fort Hood in Texas. Active shooter events at military installations over the past several years have resulted in the Installation Exercise Program Office designing an active shooter scenario and integrating into the training schedule. (N.H. Air National Guard photo by Tech. Sgt. Mark Wyatt/RELEASED)