U.S. Army Lt. Col. (Ret.) Dave Grossman (right), signs a book for Col. Phil Stewart, 9th Reconnaissance Wing commander, at the base theater Beale Air Force Base, Calif., April 2, 2014. Grossman is a former paratrooper, Army ranger, infantry commander, professor of military science and a West Point psychology professor who used his experiences to become the founder of Killology. (U.S. Air Force photo by Senior Airman Allen Pollard/Released)