The US military service dogs we used in Nam were left in Nam, and killed when no longer needed.

This statement is not entirely true, and misleading. The dogs used by doghandlers, were trained for/with the handler and ONLY the handler. They would have been of no use otherwise. If something happened to the handler, (WIA-KIA), the dog was shot because it was a threat to everyone else, and would not respond to any orders not given by his handler, as was its job.