BACKSTAGE Defense Secretary Robert M. Gates talks to a veteran before he addresses the crowd gathered to mark Rolling Thunder at the National Mall, May 29, 2011. Rolling Thunder is an annual event in which thousands of veterans ride motorcycles through the city to call attention to prisoners of war and those missing in action. SHARE: Download: Full Size (0.06 MB) Credit: VIRIN: 830519-J-SIE38-469.jpg Photo Gallery