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A 20-Gbps undersea fiber-optic cable isn't much use when you're cruising in a diesel-powered submarine. In fact, as far as the US Navy is concerned, the most important two-thirds of the planet is unwired – the part beneath the waves. Seawater interferes with electromagnetic signals, and subs usually have to raise an antenna to the surface to send and receive email – hardly a stealth maneuver. But in a recent test, the research sub USS Dolphin successfully sent a series of emails from 400 feet deep, the first time a moving vessel at that depth has been able to communicate without giving away its position. The emails were transmitted as sound waves via an acoustical modem developed by Benthos (www.benthos.com), a company based in Cape Cod. The acoustic signal, carrying data at up to 2.4 Kbps, reached a buoy where a transducer converted it to radio and beamed it line-of-sight to a ship, which sent it to dry land. The system faces a bigger test during the Seaweb 2001 exercises off the coast of San Diego: The Dolphin will cruise through an area seeded with 40 communications nodes to find out whether a continuous signal can be maintained as the sub travels from cell to cell. The military app is clear, but the U-boat Net could also be useful in undersea oil exploration and environmental research.Go Back to Top. Skip To: Start of Article.