The 3d Medical Battalion was originally organized as the 3d Sanitary Train in 1917. During World War I, it served with the 3d Division and distinguished itself in the battles of the Aisne, Champagne, Champagne-Marne, Aisne-Marne, St. Mihiel and Meuse-Argonne. The 3d Sanitary Train was re-organized as the 3d Medical Regiment in 1921 and as the 3d Medical Battalion in 1939.