The United States 32nd Infantry Division was formed from Army National Guard units from Wisconsin and Michigan and fought primarily during World War I and World War II. With roots as the Iron Brigade in the American Civil War, the division's ancestral units came to be referred to as the Iron Jaw Division. During tough combat in France in World War I, it soon acquired from the French the nickname Les Terribles, referring to its fortitude in advancing over terrain others could not. It was the first allied division to pierce the German Hindenburg Line of defense, and the 32nd then adopted its shoulder patch; a line shot through with a red arrow, to signify its tenacity in piercing the enemy line. It then became known as the Red Arrow Division.