Sixty years ago, this duo were communicating up to 1500 feet from ship to shore thanks to a pair of devices dubbed the Terraquaphone. The plans for constructing the came from the September 1961 issue of Electronics Illustrated.

The device relied on a principle we’ve seen before, namely the use of earth currents. Each Terraquaphone consisted of a three-transistor audio amplifier. Despite the name shown on the cover, it wasn’t a radio. It simply sent the audio signals through the earth, using two probes. If the probes were placed 30 feet apart, the resulting range would be 1500 feet. Of course, that depended a lot on soil and water conductivity. When it was tested in Arizon, the maximum range achieved was 600 feet.

The magazine noted that if used on a boat, one probe should be at the bow, with the other at the stern. Maximum range would be achieved with the boats parallel to one another.