 Submarines when submerged are shielded by seawater from all ordinary radio signals, and therefore are cut off from communication with military command authorities.VLF radio waves can penetrate 50-75 feet into seawater and have been used since WW2 to communicate with submarines, but the submarine must rise close to the surface, making it vulnerable to detection.In 1958, the realization that ELF waves could penetrate deeper into seawater, to normal submarine operating depths led U.S. physicist Nicholas Christofilos to suggest that the U.S. Navy use them to communicate with submarines.