The 4 U.S. Marine Heroes of the Chattanooga Tragedy

They were four people charged with the safety of others, gunned down in a place where the nation's defense is the paramount mission for those who pass through its doors. They are being deemed heroes by some, and the cruel irony of protectors becoming targets was not lost, with President Barack Obama calling it "a heartbreaking circumstance" to lose four men who served "with great valor." Here is a look at the Marines killed in what is believed to be a domestic terrorist attack on two military facilities in Chattanooga, Tennessee: