From: Interesting Engineering 

What do you do when you need to communicate with a crew of 50 sailors submerged in a submarine in an undisclosed location across the world’s oceans? That was a difficult question to answer for Navy leaders in WWII.

Radio waves don’t easily travel through saltwater, which meant that getting active communication with a submarine crew meant making the submarine surface an antenna. This was the obvious solution, but it made a previously covert submarine now a visible target.

The solution to the problem
Engineers tasked with finding a more covert solution soon discovered that radio waves with low frequencies, around 10 kHz, could penetrate saltwater to depths up to around 20 meters. They realized that if the transponders on submarines were switched to these frequency ranges, then they communicate with leadership on land.

The problem with this idea was that creating and broadcasting these low-frequency radio waves required massive antennas. Essentially, the lower the frequency of a radio wave, the longer and larger the antenna is required to be

Engineers honed in on a range of frequencies lower than 30 kHz for submarine communication. The wavelength of these frequencies were roughly 10 kilometers or more, meaning that engineers would need massive antennas. The only way to produce these frequencies with such a high range was to use a massive system of antennas with massive amounts of power.

Nazi engineers seeking to communicate with their fleet of U-boats designed the Goliath antenna network in Saxony-Anhalt, Germany. After construction, it was operated during World War II and had a transmission power of up to 1,000 kilowatts. For comparison, that’s equivalent to the power draw of 500 average American households.

The Goliath Radio Transmitter
The Goliath network would regularly transmit frequencies between 15 kHz and 25 kHz. It was powerful enough to reach any German submarine located anywhere in the world submerged up 20 meters. The only time communication was hindered was when German U-boats were navigating deep Norwegian fjords.

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