Photograph by Hulton Archive/Getty Images
A London crowd gathers to see off Maj. Edwin Richardson, a World War I pioneer in war-dog training. His bloodhounds helped locate wounded soldiers and later carried messages between outposts during artillery bombardments.
Photograph by Hulton-Deutsch Collection/Corbis
German troops take cover with a dog during World War I. The first organized military war-dog school was established in Germany in 1884.
Photograph by Underwood and Underwood, National Geographic Creative
A French sergeant and his dog wear gas masks on the front lines in World War I. On the horizon, a wounded man is carried on a stretcher. With their sensitive noses, dogs were able to smell gas attacks and bark a warning before troops could detect the chemicals.
Photograph by Bettmann/Corbis
Soldiers present dogs for induction into the U.S. Army in 1942 in Front Royal, Virginia. After Pearl Harbor, Americans were encouraged to donate their dogs to the Army. Dogs sent from all 48 states were trained for patrol, sentry duty, mine detection, and as messengers.
Photograph by W. Eugene Smith, Time & Life Pictures/Getty Images
U.S. GIs in World War II treat a combat dog wounded in the battle for Guam.
Photograph by Terry Fincher, Getty Images
U.S. Marines and a combat dog run toward a helicopter in Tay Ninh, Vietnam, in 1968. Military dogs in Vietnam led jungle patrols and sniffed out weapons caches, among other duties. Despite protests from their handlers, at war’s end the military left some 4,000 dogs behind.