 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 . 
