Project Sanguine

Clam Lake, Wisconsin ELF transmitter in 1982, part of Project ELF, the downsized successor to Sanguine. Sections of the rights of way for the power lines that make up the two 14-mile-long ground dipole antennas can be seen passing through the forest in the lower left.

Project Sanguine was a US Navy project proposed in 1968 for communication with submerged submarines using extremely low frequency (ELF) radio waves. The initially proposed system, hardened to survive a nuclear attack, would have required a giant antenna covering two-fifths of the state of Wisconsin. The proposed approach was never implemented because of protests and potential environmental impact. A smaller, less hardened system called Project ELF consisting of two linked ELF transmitters located at Clam Lake, Wisconsin 46°05′05.6″N 90°55′03.7″W / 46.084889°N 90.917694°W / 46.084889; -90.917694 and Republic, Michigan 46°20′10.1″N 87°53′04.6″W / 46.336139°N 87.884611°W / 46.336139; -87.884611 was built beginning in 1982 and operated from 1989 until 2004. The system transmitted at a frequency of 76 Hz. At ELF frequencies, the bandwidth of the transmission was very small, so the system could only send short-coded text messages at a very low data rate. These signals were used to summon specific vessels to the surface to receive longer operational orders by ordinary radio or satellite communication.