The lack of detail is disappointing, but not entirely surprising given the historical context. The SOFAR channel in the ocean transmits low frequency sound wave

The lack of detail is disappointing, but not entirely surprising given the historical context. The SOFAR channel in the ocean transmits low frequency sound waves for thousands of miles. Its existence and applications were kept classified until the 90s. https://en.wikipedia.org/wiki/SOFAR_channel https://en.wikipedia.org/wiki/SOFAR_channel