Wiktionary
war dog
n. 1 A dog that was deployed in a war. 2 A veteran soldier in a war, particularly a heroic one 3 (context figuratively English) a warrior; a battler
Usage examples of "war dog".
If his dog was going to be a properly trained war dog, he needed to be exposed to guns, blood, death, gore, and killing at the youngest possible age.
She had been trained as a war dog and only recently retired to breed more war dogs.