When was the first underwater acoustic communication system tested?

Underwater acoustic communication was tested in the early 20th century, and major developments accelerated during World War I as navies sought ways to detect submarines. Because radio waves travel poorly through seawater, sound became the primary tool for underwater signaling and detection. Later systems supported navigation, scientific instrumentation, and communication with submersibles. These technologies laid the groundwork for sonar and many modern ocean-monitoring networks. Acoustic methods remain essential in marine science and defense today.