View of an American marine as he lies in a foxhole and whistles at a husky, one of the scouting dogs used during the landing on Guam, August 1944. (Photo by W. Eugene Smith/Time & Life Pictures/Getty Images)

A U.S. Marine leads training on a shooting range in France in an undated photo taken during the First World War. (Photo by Reuters/Courtesy Library of Congress)

An interactive art installation created by artist Michael Verdon called the “Temple of Essence” dedicated to "victims of the war on drugs" is burned on the U.S. National Mall in front of the Washington Monument in Washington November 22, 2015. People were encouraged to write personal messages on the temple walls and leave mementos behind inside the interactive art piece, which was the centerpiece of a 48-hour vigil called "Catharsis on the Mall: A Vigil for Healing the Drug War". (Photo by Jim Bourg/Reuters)

The body of one of several U.S. soldiers who were executed after being captured by North Korean troops just south of Seoul in early July 1950. (Photo by AP Photo)

Models Felicia Verna and Crystal Boyd wearing Stacey Angela during the Fallen Hearts Fashion Experience at Symphony Space on May 31, 2011 in New York City. (Photo by Jemal Countess/Getty Images)

A Republican farmer defending a farm on the outskirts of Irun against Nationalist forces during the Spanish Civil War, 6th September 1936. A comrade lies dead by his side. (Photo by Keystone/Hulton Archive/Getty Images)

Mark Trotter and Luke Thompson of New Zealand compete in the Senior Prearranged Sparring on the final day of the 2011 ITF Taekwon-Do World Championships at TSB Bank Arena on March 13, 2011 in Wellington, New Zealand.

Harry Sprinkle eats a meal at St. John's Bread and Life, a free meal service, on December 23, 2011 in the Brooklyn borough of New York City. St. John's Bread and Life serves approximately 2,200 meals per day; the organization has existed since 1982. (Photo by Andrew Burton/Getty Images)