The 309th Infantry Regiment was constituted in the National Army on August 5, 1917, and assigned to the 78th Division ("Lightning Division") during World War I. The regiment participated in major operations, including the Meuse-Argonne Offensive, helping to break German defensive lines. Reactivated for World War II, the 309th fought in campaigns across France, Belgium, and Germany, contributing to the liberation of Europe. After the war, the regiment underwent several reorganizations and today serves as a training unit in the U.S. Army Reserve, continuing its legacy of service.