Webb was commissioned an army officer in June 1942 and became a personal aide to General Lloyd R. Fredendall who was commander of the II Corps (United States). Webb accompanied Fredendall to England in October 1942 and participated in the invasion of North Africa in November 1942 when the Second Corps captured the city of Oran. The Second Corps then attacked eastward into Tunisia. In February 1943 the German army launched a counterattack at Kasserine Pass which repulsed the Second Corps and nearly broke through the Allied lines. The Supreme Commander Dwight D. Eisenhower relieved Fredendall of command in March 1943 and sent him back to the United States where he became deputy commander of the Second United States Army at Memphis, Tennessee.
Webb returned to the United States with Fredendall and later served in the European Theater. Webb left the Army after the war and returned to Hollywood, California, where he continued his work as a screenwriter. He died on September 27, 1974.