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This featured in the series Sixty Years Ago in November, 1980.
Until shortly before 1920 communication between submarines and shore or other vessels was only possible while transmitting or receiving above the waves, due, of course, to the attenuation of electromagnetic waves by water. An article called 'The Submarines Wireless' in the November 27th, 1920 edition described newly found techniques which enabled practical communication while the vessel was under water. The techniques in question involved the development of extremely sensitive receiving and amplifying apparatus, and more efficient aerial systems, to make possible the bridging of distances of up to three miles while the vessel was submerged under nine feet of water. An aerial current of six amps was required for this feat, but there is no mention of the frequencies used, although long-waves are suggested as they were found to be able to penetrate the water better than short-waves.
In the same issue, a small feature also appeared on a wireless telephone pack-set which was used by RAF officers as far back as the autumn of 1918. Two photos show the set 'mounted' on an officer who stands, supported by his bicycle, with a wooden frame aerial projecting from the top of his head. As wireless sets, especially of this type, were not all that common at that time he probably gave some of the locals quite a start.
The need for ships to pass out of unlit harbours during wartime was the necessity that gave birth to the invention of the 'radio cable', which was discussed in the 'Notes and News' section also in this issue. This guidance cable, through which an alternating current was passed, was laid in the harbour waterways. Ships using the cable were fitted with two detection coils, probably one on either side of the deck, which intercepted the electromagnetic waves coming from the cable. By noting the relative strength of the waves reaching each coil, it was possible for the ships navigator to determine his position in relation to the cable. The US Navy laid one such cable which was sixteen miles in length, in the main waterway approaching the port of New York.
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