extremely low frequencies

Early submarine warfare exposed a major communications gap for submerged boats.

The article traces submarines from Civil War-era prototypes to World War I U-boats and early U.S. Navy craft.

Engineers tried radios onboard, seawater conduction, and submerged brass plates, but seawater largely blocked signals.

Those failures led to limited fixes such as floating antenna buoys and other workarounds that shaped later underwater communication design.