In anticipation of U.S. entry into World War II, Girard was among thousands of reservists and National Guard members called to active duty in 1940. He completed the Infantry Officer Basic and Advanced Courses, and served initially as a platoon leader in the 82nd Armored Reconnaissance Battalion at Fort Benning, Georgia. His battalion was part of the 2nd Armored Division, and Girard rose to captain and commander of a company as his battalion served in the Mediterranean and European Theaters of Operations. He took part in the Tunisia, Sicily, Normandy, Northern France, Rhineland, Ardennes, and Central Europe campaigns, and he was battalion commander with the rank of major at the end of the war.