On the land, the radio is usually used in no cable communication. The absorption and attenuation of
underwater radio are large. No matter how far the transmission distance, can only use large antennas and high
transmission power, or can not complete underwater communications tasks. Compared to all kinds of known
as form of energy, the only sound waves in the underwater spread for best performance, which allows to
sound waves as the carrier of the underwater acoustic communication become the mainstream of the
underwater communication. In 1945 the earliest underwater speech communication system had been
developed by the United States navy underwater acoustic laboratory. This system was used in the
communication between the submarines, which used single side band modulation with carrier frequency 8~11
kHz, work distance a few kilometers.