The Labrador Retriever, Labrador or just Lab, is a medium-large breed of retriever-gun dog. The Labrador is the most popular breed of dog in many nations. The Vietnam War is the only war in American history in which US war dogs, which were officially classified by the military as 'military working dogs,' were not allowed to officially return home after the war. Classified as expendable equipment, of the approximate 4,000 US K-9s deployed to the Vietnam War, it is estimated that only about 200 US war dogs survived Vietnam to be put into service at other outposts stationed overseas. Aside from these 200 or so, the remaining canines who were not killed in action were either euthanized or left behind.