Most Americans are aware of the era of lawlessness in this country that began with the passage of the Eigh-teenth Amendment to the Constitution in 1919. The institution of Prohibition brought with it major law enforcement problems, whose effects continue to be felt today. Few people, how-ever, are aware of the major role played by communications intel-ligence in the enforcement of the Prohibition laws. The files of the United States Coast Guard (USCG) and the Federal Communica-tions Commission (FCC), including the files of the Radio Division of the Department of Commerce, show that radio was used on a large scale in connection with rum-running activities. The radio opera-tions of the rum-running organizations were, in fact, comparable in size, technical skill, and organization with the radio operation that would be conducted by enemy agents in World War II.