Soldiers, including two recruits who have brought some chickens, at Victoria prepare to board the train for the battle front. (Photo by Hulton Archive/Getty Images)

An American soldier walks ahead of an MKIV (Mark IV) British-made tank, circa 1918. (Photo by Hulton Archive/Getty Images)

Throughout the course of the long war in Afghanistan, Coalition troops have relied on thousands of military working dogs to help keep them safe, and make their jobs easier. The dogs are trained to detect explosives, to find illegal drugs, to search for missing comrades, or target enemy combatants. Not only are they active on the front lines, but behind the lines they serve as therapy dogs, service dogs, and loyal companions. They also share the same risks as the ground troops, suffering injuries and sometimes death on the battlefields. Gathered here are images of these dogs and their handlers in Afghanistan and back home, from over the past several years, part of the ongoing series here on Afghanistan.

Kazakh troops march during a parade of the armed forces to mark the Defender of the Fatherland Day in Astana, May 7, 2014. (Photo by Mukhtar Kholdorbekov/Reuters)

In this January 31, 2014 file photo released by the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), shows residents of the besieged Palestinian camp of Yarmouk, queuing to receive food supplies, in Damascus, Syria. That year, the U.N. was able to deliver food to about five percent of people in besieged areas including Yarmouk, while today estimates show the organization is reaching less than one percent. (Photo by UNRWA via AP Photo)

A decorated elephant march at the Navam Perahera, a Buddhist pageant of elephants, dancers and drummers, in Colombo February 3, 2015. Over 50 elephants participated in the street parade for Gangaramaya temple's annual Perahera festival, along with a nightly procession of traditional dancers, fire twirlers and traditional musicians. (Photo by Dinuka Liyanawatte/Reuters)

Veterans of the Bangladesh war of liberation march past during the celebration of the country’s 45th Victory Day at the national parade ground in Dhaka December 16, 2015. (Photo by Ashikur Rahman/Reuters)

Two guards perform an execution in China, one holding the gun, the other holding a mask over the victim's face. (Photo by General Photographic Agency/Getty Images). Circa 1925