Until 2000, with a few exceptions, working dogs used by the military were considered equipment and their welfare and transport were handled by the same simple cost/benefit calculations used when disposing of a well used truck. If it was deemed cheaper to leave them behind and buy another they were left behind if extraordinary efforts were not made. Some handlers were forced to quite literally steal their dogs, or report them lost in combat, and find unofficial ways of shipping them home. Too often they were left behind with little or no provisions being made for them.

Some of this goes back to the rules established in early in the formation of the US military for procurement and maintenance of livestock. Well into WW2, mainly in the Burma and Italian campaigns, the US military was purchasing and maintaining service animals in the form of horses, mules and donkeys in addition to some dogs. This wasn't unusual and the German army was still using horses in large numbers through to the end of the war in Europe. The common view during that time was that these horses and mules were entirely expendable to be used as transport or food, or liquidated at will.

I'm not saying any or all of this was a good thing. Acceptance of routine abuse of animals is a sign of a society that is also willing to abuse humans. Insensitivity and a lack of empathy is an expression of our dealing with others. Torture of animals is one of the defining behaviors of sociopaths.