A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

A Russian trenchmortar crew run to take up a new firing position in the Stalingrad area during the Great Patriotic War. (Photo by Keystone/Getty Images). October 1942

A German Air Force Officer sits astride a dead boar outside a house where he is stationed near the Western Front, in this 1918 handout picture. This picture is part of a previously unpublished set of World War One (WWI) images from a private collection. The pictures offer an unusual view of varied and contrasting aspects of the conflict, from high tech artillery to mobile pigeon lofts, and from officers partying in their headquarters to the grim reality of life and death in the trenches. The year 2014 marks the centenary of the start of the war. (Photo by Reuters/Archive of Modern Conflict London)

An American Marine readies to land on Guadalcanal during the five-month struggle for the island between late 1942 and early 1943. Three thousand miles south of Tokyo, Guadalcanal was a major shipping point for military supplies. The Allied victory there in February, 1943, marked a major turning point in the war after a string of Japanese victories in the Pacific. (Photo by Joe Scherschel/Time & Life Pictures)

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)

These Arab recruits line up in a barracks square in the British Mandate of Palestine, on December 28, 1940, for their first drill under a British solider. Some 6,000 Palestinian Arabs signed up with the British Army during the course of World War II. (AP Photo)

A recruitment drive during the First World War at Trafalgar Square, London. (Photo by Central Press/Getty Images)

Military helicopters fly in formation above a billboard with a picture of China's late Chairman Mao Zedong during a training session for the upcoming parade marking the 70th anniversary of the end of World War Two, on the outskirts of Beijing, July 2, 2015. Troops from Russia and Mongolia will march together with Chinese forces in a parade in Beijing in September to commemorate the end of World War Two, the government and state media said on Thursday, confirming the first two foreign participants. (Photo by Jason Lee/Reuters)