World War I | 1917: Young servicemen bring mistletoe to a London YMCA center preparing for Christmas celebrations in honor of American troops stationed there. | (Topical Press Agency/Getty Images)

World War II | 1939: A member of the Auxiliary Territorial Service in Britain kisses a soldier under a sprig of mistletoe. | (Hulton-Deutsch Collection/CORBIS)

World War II | 1940: A group of soldiers break from clearing London’s air raid sites to have some Christmas pudding. | (William Vanderson/Fox Photos/Getty Images)

World War II | 1940: Women offer tea to members of the Home Guard who are on patrol over Christmas. | (Hulton-Deutsch Collection/CORBIS)

World War II | 1944: American soldiers working in the army kitchen gather around a decorated rotary sink to peel potatoes. | (Bettmann/CORBIS)

World War II | 1944: Servicemen aboard the USS Lexington celebrate Christmas with make-shift paper decorations and by dressing a fellow soldier up as Santa Claus (in a firefighting suit). | (CORBIS)

Korean War | 1950: An Australian corporal enjoys his Christmas turkey dinner while stationed near the front line. | (Keystone/Getty Images)

Korean War | 1954: U.S. troops pass out Christmas gifts and letters sent from home. | (Bettmann/CORBIS)

Vietnam War | 1969: U.S. soldiers set up a Christmas tree in a spare mortar pit at the Duc Lap Special Forces camp. | (Bettmann/CORBIS)

Vietnam War | 1970: Pfc. James Heckman, 20, of Kalamazoo, Michigan, reads a letter attached to the Christmas present he received while stationed in Con Thein, Vietnam. | (Bettmann/CORBIS)