Ambrose Channel pilot cable
Delays posed a major problem for shipping en route to New York City, and bad weather could close the channel for days.
[4] It was powered by a generator at Fort Lafayette that produced 500 Hz (cycles per second) current at 400 volts, resulting in an alternating electromagnetic field along the length of the cable that could be detected to approximately a thousand yards away.
Around the same time Charles Stevenson patented a means of navigating ships over an electrically charge cable using a galvanometer.
The method became practical when Earl Hanson adapted early vacuum tube circuits to amplify the signal.
[9] Robert H. Marriott was a radio pioneer employed by the Navy in Puget Sound, where he conducted early experiments with underwater pilot cables.
[11] In October, 1919 Commander Hooper instructed A. Crossley, an expert radio aid, to develop and test the concept on a larger scale at the New London Naval Base.
[25] The ship's windows were covered with canvas and the captains took turns navigating using only the audio cues from the cable.
[32] The cable itself was paid for using public funds, but it was the responsibility of ship owners to outfit their vessels with receiving equipment.
[35] Radio Broadcast expressed the belief that navigation cables would become common for both ships and aircraft: "...there is a future for the audio cable... Its fullest usefulness at American ports and elsewhere waits, however, on that large appreciation of radio devices for sea as well as air navigation which pilots, both on the sea and in the air, expect, but do not as yet demand.
"[36] Despite the media hype, it appears that the Ambrose Channel pilot cable never met with large scale commercial success.
[41] By 1930, an article in the Journal of the Royal Society of Arts declared that "wireless aids and echo sounding have superseded [the leader cable]".
Earl Hanson, one of the key players in designing the Ambrose Channel cable, writing for Popular Mechanics, viewed it as a step toward applying radio cable technology in vast swaths of everyday life, including guiding aircraft and navigating and powering automobiles.
