The use of dogs in warfare dates back to the late antiquity of the Greco-Roman world. Attila the Hun used large Molosser breeds in his campaigns. When the British attacked the Irish, they used dogs to fight, and the Irish in turn used Irish Wolfhounds to attack knights on horseback. In the 20th century, dogs' duties became more diverse. In World War I, dogs were used to locate wounded soldiers in the trenches and even had their own gas masks. Russian units trained dogs to carry bombs under invading tanks, and many armies used them as messengers. In World War II and Vietnam, scout dogs helped locate the enemy in dense jungles. Today, dogs are used to sniff out explosives and find hidden munitions, while attack dogs accompany many military police units. The U.S. Army assigns each dog a rank, one higher than that of their handler, and when the handler is promoted, the dog is promoted as well.