page_title: Ambrose Channel pilot cable
section_title: Research and development
hierarchical_section_title: Ambrose Channel pilot cable / Research and development
caption_attribution_description: Circuit diagram two-stage ("2 step") vacuum-tube amplifier used circa 1921 in conjunction with the w:Ambrose Channel pilot cable.
context_page_description: 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 port at times 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.
context_section_description: The pilot cable required a series of prior discoveries and inventions. In 1882,  A. R. Sennett patented the use of a submerged electrical cable to communicate with a ship at a fixed location. 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.
  Robert H. Marriott was a radio pioneer employed by the Navy in Puget Sound, where he conducted early experiments with underwater pilot cables. His results were sufficiently promising that he recommended further development to Commander Stanford C. Hooper.  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. Crossley installed a longer version of the cable that Marriott had designed. He used a wooden hulled launch for the first round of tests before moving to a steel-hulled submarine for later tests. Both types of vessel picked up the signal and followed the underwater test cable without problem.
caption: Two-stage vacuum-tube amplifier alternately takes input from inductance coils (top) hung on each side of ship.[8]
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