Southern Defense Command (SDC) was established on 17 March 1941 as the command formation of the U.S. Army responsible for coordinating the defense of the Gulf of Mexico coastal region of the United States. A second major responsibility of SDC was the training of soldiers prior to their deployment overseas. The first Commanding General of SDC was Lieutenant General Herbert Brees, who continued on in command of the Third U.S. Army. SDC headquarters was co-located with the existing Third Army headquarters at Fort Sam Houston. SDC's operational region covered the states of New Mexico, Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Tennessee, and the western half of the Florida Panhandle.