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Radio waves can’t be transmitted through water, but submarines can now
transmit e-mails without having to surface and reveal their location. Using an
“acoustic modem” that pumps out pressure waves, the US Navy sub USS Dolphin,
travelling at a depth of 120 metres, sent e-mail consisting of text and pictures
over a distance of 5 kilometres at 2.4 kilobits per second to a radio buoy. This
subsequently relayed the message to shore. However, the Navy’s research comes at a time
when the effect of underwater acoustic transmissions on sea life is ringing alarm bells
(see “Ear-splitting sonar”).