Communication with submarines Communication with submarines is difficult because radio waves do not travel well through good electrical conductor s like salt water . The obvious solution is to surface and raise an antenna above the water , then use ordinary radio transmissions . However , a submarine is most vulnerable when on the surface . Early submarines had to surface frequently for oxygen needed by their diesel engines to charge their batteries . During the Cold War , however , nuclear - powered submarines were developed that could stay submerged for months . To communicate with submerged submarines several techniques are used . Acoustic transmission . Sound travels far in water , and underwater loudspeaker s and hydrophone s can cover quite a gap . Apparently , both the American ( SOSUS ) and the Russian Navy have placed sonic communication equipment in the seabed of areas frequently traveled by their submarines and connected it by underwater communications cable s to their land stations . If a submarine hides near such a device , it can stay in contact with its headquarters . An underwater telephone sometimes called Gertrude is also used to communicate with submersibles . Very low frequency . VLF radio waves ( 3 – 30 kHz ) can penetrate seawater to a depth of approximately 20 meters . Hence a submarine at shallow depth can use these frequencies . A vessel more deeply submerged might use a buoy on a long cable equipped with an antenna . The buoy rises to a few meters below the surface , and may be small enough to remain undetected by enemy sonar / radar . Due to the low frequency a VLF broadcast antenna needs to be quite big . In fact , broadcasting sites are usually a few square kilometres . This prevents such antennas being installed on submarines . Submarines only carry a VLF reception aerial , and do not respond on such low frequencies . So a ground - to - submarine VLF broadcast is always a one way broadcast , originating on the ground and received aboard the boat . If two - way communication is needed , the boat must ascend to periscope depth ( just below the surface ) and raise a telescopic mast antenna to communicate on higher frequencies ( such as HF , UHF or VHF ) . Because of the narrow bandwidth of this band , VLF radio signals cannot carry audio ( voice ) , and only transmit text messages at a slow data rate . VLF data transmission rates are around 300 bit / s - or about 35 8 - bit ASCII characters per second ( or the equivalent of a sentence every two seconds ) - a total of 450 words per minute . Simply shifting to 7 - bit ASCII increases the number of transmitted characters per time unit by 14 % . An additional shift to a 6 - bit or a 5 - bit code ( such as the baudot code ) would result in speeds of more than 600 and 700 words per minute . Extremely low frequency . Electromagnetic waves in the ELF frequency range ( 3 – 300 Hz ) ( see also SLF ) can penetrate seawater to depths of hundreds of meters , allowing communication with submarines at their operating depths . Building an ELF transmitter is a formidable challenge , as they have to work at incredibly long wavelength s : The US Navy ' s system , Seafarer , which was a variant of a larger system proposed under the codename Project Sanguine , operated at 76 hertz , the Soviet / Russian system ( called ZEVS ) at 82 hertz . The latter corresponds to a wavelength of 3 , 658 . 5 kilometers . That is more than a quarter of the Earth ' s diameter . Obviously , the usual half - wavelength dipole antenna cannot be constructed , as it would spread across a large country . Instead , one has to find an area with very " low " ground conductivity ( a requirement opposite to usual radio transmitter sites ) , bury two huge electrodes in the ground at different sites , and then feed lines to them from a station in the middle , in the form of wires on poles . Although other separations are possible , 60 kilometers is the distance used by the ZEVS transmitter located near Murmansk . As the ground conductivity is poor , the current between the electrodes will penetrate deep into the Earth , essentially using a large part of the globe as an antenna . The antenna length in Republic , Michigan was approximately . The antenna is very inefficient . To drive it , a dedicated power plant seems to be required , although the power emitted as radiation is only a few watts . Its transmission can be received virtually anywhere . A station in Antarctica at 78°S 167°W detected transmission when the Soviet Navy put their ZEVS antenna into operation . Due to the technical difficulty of building an ELF transmitter , only the US and the Russian Navy owned such systems . Until it was dismantled in late September 2004 , the American " Seafarer " , later called " Project ELF " system ( 76 Hz ) consisted of two antennas , located at Clam Lake , Wisconsin ( since 1977 ) and at Republic , Michigan in the Upper Peninsula ( since 1980 ) . The Russian antenna ( " ZEVS " , 82 Hz ) is installed at the Kola Peninsula near Murmansk . It was noticed in the West in the early 1990s . The British Royal Navy once considered building their own transmitter at Glengarry Forest , Scotland , but the project was canceled . ELF transmissions . The coding used for US military ELF transmissions employed a 64 - symbol Reed - Solomon error correction code , meaning that the alphabet had 64 symbols , each represented by a very long pseudo - random sequence . The entire transmission was then encrypted . The advantages of such a technique are that by correlating multiple transmissions , a message could be completed even with very low signal - to - noise ratio s , and because only a very few pseudo - random sequences represented actual message characters , there was a very high probability that if a message was successfully received , it was a valid message ( anti - spoofing ) . The communication link is one - way . No submarine could have its own ELF transmitter on board , due to the sheer size of such a device . Attempts to design a transmitter which can be immersed in the sea or flown on an aircraft were soon abandoned . Due to the limited bandwidth , information can only be transmitted very slowly , on the order of a few characters per minute ( see Shannon ' s coding theorem ) . Thus it is reasonable to assume that the actual messages were mostly generic instructions or requests to establish a different form of two - way communication with the relevant authority . Standard radio technology . A surfaced submarine can use ordinary radio communications . Submarines may use naval frequencies in the HF , VHF and UHF ranges ( i . e . , bands ) , and transmit information via both voice and teleprinter modulation techniques . Where available , dedicated military communications satellite systems are preferred for long distance communications , as HF may betray the location of the submarine . The US Navy ' s system is called " Submarine Satellite Information Exchange Sub - System " ( SSIXS ) , a component of the " Navy Ultra High Frequency Satellite Communications System " ( UHF SATCOM ) .