Air Force airmen provide security through a neighborhood in Moore, Okla., May 22, 2013, after a devastating tornado killed dozens of people there, May 20. The airmen are assigned to the 146th Air Support Squadron, Will Rogers Air National Guard Base. U.S. Air Force photo by Staff Sgt. Caroline Hayworth

Retired Army Spc. Luis Puertas wins the men's 100-meter above-the-knee single- and double-amputations event during the 2013 Warrior Games in Colorado Springs, Colo., May 14, 2014. DOD photo by EJ Hersom

A paratrooper weaves through a ladder obstacle while competing in a team assault obstacle course competition that is part of the 82nd Airborne Division's All-American week celebration on Fort Bragg, N.C., May 21, 2013. U.S. Army photo by Sgt. Michael J. MacLeod

U.S. Defense Secretary Chuck Hagel speaks with John Chipman, director and chief executive of International Institute for Strategic Studies, at the Shangri-La Dialogue in Singapore, June 1, 2013. Hagel will discuss issues of mutual importance with defense ministers at the event and then travel to Brussels to meet with NATO defense ministers. DOD photo by Erin A. Kirk-Cuomo

U.S. Defense Secretary Chuck Hagel speaks at the opening plenary session of the Shangri-La Dialogue in Singapore, June 1, 2013. Hagel will discuss issues of mutual importance with defense ministers at the event and then travel to Brussels to meet with NATO defense ministers. DOD photo by Erin A. Kirk-Cuomo

U.S. Defense Secretary Chuck Hagel greets South Korean Defense Minister Kim Kwan-jin before the opening plenary session at the Shangri-La Dialogue in Singapore, June 1, 2013. Hagel will discuss issues of mutual importance with defense ministers at the event and then travel to Brussels to meet with NATO defense ministers. DOD photo by Erin A. Kirk-Cuomo

U.S. Defense Secretary Chuck Hagel speaks with British Defense Minister Philip Hammond at the opening plenary session of the Shangri-La Dialogue in Singapore, June 1, 2013. Hagel will discuss issues of mutual importance with defense ministers at the event and then continue to Brussels to meet with NATO defense ministers. DOD photo by Erin A. Kirk-Cuomo

U.S. Defense Secretary Chuck Hagel speaks at the opening plenary session of the Shangri-La Dialogue in Singapore, June 1, 2013. Hagel will meet with defense ministers at the event to discuss issues of mutual importance and then continue to Brussels to meet with NATO defense ministers. DOD photo by Erin A. Kirk-Cuomo