https://en.wikipedia.org/wiki/CONELRAD
U.S. president Harry S. Truman established CONELRAD in 1951. After the development of intercontinental ballistic missiles reduced the likelihood of a bomber attack, and the development of superior navigation systems that did not rely on radio direction finding for use in those bomber aircraft which were sent against the United States, CONELRAD was replaced by the Emergency Broadcast System (EBS) on August 5, 1963, which was later replaced by the Emergency Alert System (EAS) on January 1, 1997; all have been administered by the Federal Communications Commission (FCC).[1]