Surveillance camera video of Aaron Alexis, a contractor who killed 12 people at the Washington Navy Yard on Sept. 16, 2013. Alexis was one of thousands of individuals cleared by the firm known as USIS. HO/UPI/Landov hide caption

itoggle caption HO/UPI/Landov

King George VI and Queen Elizabeth arrive at the Washington Navy Yard on June 9, 1939, to join President Franklin Roosevelt on a cruise down the Potomac River to Mount Vernon, Va. AP hide caption

itoggle caption AP