Ambrose Channel pilot cable

The Ambrose Channel pilot cable, also called the Ambrose Channel leader cable, was a cable laid in Ambrose Channel at the entrance to the Port of New York and New Jersey that provided an audio tone for guiding ships in and out of the port during periods of low visibility. The cable was laid during 1919 and 1920; it had been removed from the channel and replaced by wireless technology by the end of the 1920s.

Source: Wikipedia — Ambrose Channel pilot cable (CC BY-SA 4.0)