Citations, many times they were used in combat, google

 2100 BC Hammurabi equipped his warrior with huge dogs.
 628 BC Lydians deployed a separate battalion of fighting dogs.
 525 BC Kambyses 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.
 50 AD Rome conquers Britain giant fighting dogs are discovered and exported for the Colosseum.
 101 AD Battle of Vercellae large Kimber dogs led by women defend their laagers.
 101 AD Romans employ one dog fighting company per legion.
 1525 AD Henry VIII exports 400 Mastiffs to support Spain.
 1580 AD Elizabeth I sends 800 fighting dogs to fight in the Desmond Rebellions.
 1799 AD Napoleon assembles large numbers of fighting dogs in front of his reserves.