In the 1960s, US Navy officials concocted an ambitious plan: they wanted to bury a gigantic grid of cables under roughly 41 percent of the state of Wisconsin in order to turn its bedrock into the world’s largest radio antenna.
The plan was called Project Sanguine. And though it sounds crazy, it was a logical — albeit impractical — way of communicating with deep-sea submarines around the world.
The problem was that radio waves don’t travel well through water, so there was no good way to send signals to the nuclear-powered subs that stayed submerged for months at a time during the Cold War. Project Sanguine would have been an antenna for transmitting extremely low-frequency (ELF) waves that can penetrate water and reach the subs.
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