The US Navy has been in business since 1798. In the days of sail, the bosun's mate of the watch would use his whistle to pass orders. When ships became electrified, information and orders could be passed over the 1st Main Circuit, the "1MC". By tradition, the bos'n's whistle is still blown at the beginning of an announcement over the 1MC public address system, followed by the words Now Hear This.