Sergeant Stubby was the most decorated war dog of World War I and the only dog to be promoted to sergeant through combat. The Boston Bull Terrier started out as the mascot of the 102nd Infantry, 26th Yankee Division, and ended up becoming a full-fledged combat dog. Brought up to the front lines, he was injured in a gas attack early on, which gave him a sensitivity to gas that later allowed him to warn his soldiers of incoming gas attacks by running and barking. He helped find wounded soldiers, even captured a German spy who was trying to map allied trenches. Stubby was the first dog ever given rank in the United States Armed Forces, and was highly decorated for his participation in seventeen engagements, and being wounded twice.
via The Atlantic