Dogs have been used in warfare starting in prehistoric times. Dogs have been trained in combat, used as guard dogs, trackers and used to find hidden items, like mines. Some war dogs were simply companions or mascots to solders and generals alike. War dogs were used by the Egyptians, Greeks, Romans, Persians, and Britons in a wide variety of rolls.

The Romans used entire formations of hundreds of dogs to attack the enemy. They were even given leather and chain mail armor, and spiked collars. The Molossians (a tribe from what is now Greece) had the largest strongest dogs know to the ancient Romans, which they called "Canis Molosus" ("Canis" is Latin for "dog" and where the term "canine" comes from). This was the most powerful dog known to the Romans until the met the mastiff of the Britons. The Romans loved the mastiff and took several back to Rome and began breeding them. Though historical evidence is much harder to come by, it is believed that Native Americans also used dogs in warfare.

During the Late Antiquity, Atilla the Hun used giant Molosser dogs in his campaigns. Gifts of war dog breeding stock between European royalty were seen as suitable tokens for exchange throughout the Middle Ages. Other civilizations used armored dogs to defend caravans or attack enemies. The Spanish conquistadors used armored dogs that had been trained to kill and disembowel when they invaded the land controlled by South American natives. The British used dogs when they attacked the Irish and the Irish in turn used Irish Wolfhounds to attack invading Norman knights on horseback. Two wolfhounds, or even a single one were often capable of taking a mounted man in armor off his horse, where the lightly armed handler would finish him off if necessary. Fredrick the Great used dogs as messengers during the Seven Years War. Napoleon used dogs and dogs were used in French shipyards as guards

The use of dogs in warfare has been common even in many early civilizations. As warfare has progressed, their purposes have changed greatly. Some examples are:

* 628 BC: The Lydians deployed a separate battalion of fighting dogs.

* 525 BC: Cambyses II used huge fighting dogs against Egyptian spearmen and archers.

* 490 BC: Battle of Marathon: A brave fighting dog was immortalized in a mural.

* 385 BC: Siege of Mantineia: Fighting dogs cut off enemy reinforcements.

* 101 BC: Battle of Vercellae: Large Cimbri dogs led by women defended their laagers.

* 1525: Henry VIII exported 400 mastiffs to support Spain.

* 1580: Elizabeth I sent 800 fighting dogs to fight in the Desmond Rebellions.