Sergeant Stubby

Sergeant Stubby (1916 or 1917 – March 16, 1926), was the most decorated war dog of World War I and the only dog to be promoted to sergeant through combat.  He saved his regiment from surprise mustard gas attacks, located and comforted the wounded, and even once caught a German spy by the seat of his pants. Back home his exploits were front page news of every major newspaper. Stubby served with the 102nd Infantry, 26th (Yankee) Division in the trenches in France for 18 months and participated in four offensives and 17 battles.

Source: wikipedia