Communication with submarines
Encyclopedia
Communication with submarine
s is difficult because radio waves
do not travel well through thick electrical conductor
s like salt water.
The obvious solution is to surface and raise an antenna above the water, then use ordinary radio transmissions. Early submarines had to frequently surface anyway for the oxygen needed by their diesel engines. During the Cold War, however, nuclear-powered submarines were developed that could stay submerged for months. In order to allow for communication with submerged submarines, several techniques are used.
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.
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 kilometers (or miles). This of course 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 surface and communicate on other, higher, frequencies (such as UHF or VHF).
This band allows for a roughly 300 bit/s transmission - 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 results in a baud rate (characters per second) increase of 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.
Electromagnetic waves in the ELF
frequency range (3–30 Hz
) (see also SLF
) can travel through the oceans and reach submarines anywhere. Building an ELF transmitter is a formidable challenge, as they have to work at incredibly long wavelength
s: The US Navy's system (called Seafarer
) operated at 76 hertz
, the Soviet/Russian system (called ZEVS
) at 82 hertz. The latter corresponds to a wavelength of 3658.5 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 52 kilometres (32.3 mi). 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 watt
s. Its transmission can be received virtually anywhere. A station in Antarctica at 78°S 167°W noticed when the Soviet Navy put their ZEVS antenna into operation.
Due to the technical difficulty of building an ELF transmitter, only the USA 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). Before 1977, the Sanguine system was used, placed in the Laurentian Shield in Wisconsin
. 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.
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.
, VHF and UHF voice and teleprinter circuits. 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).
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s is difficult because radio waves
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...
do not travel well through thick electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s like salt water.
The obvious solution is to surface and raise an antenna above the water, then use ordinary radio transmissions. Early submarines had to frequently surface anyway for the oxygen needed by their diesel engines. During the Cold War, however, nuclear-powered submarines were developed that could stay submerged for months. In order to allow for communication with submerged submarines, several techniques are used.
Acoustic transmission
SoundSound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
travels far in water, and underwater loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s and hydrophone
Hydrophone
A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...
s can cover quite a gap. Apparently, both the American (SOSUS
SOSUS
SOSUS, an acronym for Sound Surveillance System, is a chain of underwater listening posts across the northern Atlantic Ocean near Greenland, Iceland and the United Kingdom — the GIUK gap. It was originally operated by the United States Navy for tracking Soviet submarines, which had to pass...
) 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
Submarine communications cable
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean....
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
Underwater telephone
The underwater telephone also known as UQC , or Gertrude wasdeveloped by the U.S. Navy in 1945 , the UQC underwater telephone is used on all manned submersibles in operation. Voices communicated through the UQC are heterodyned to a high pitch for acoustic transmission through water....
is also used to communicate with submersibles.
Very low frequency
Very low frequency
225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...
radio waves (3–30 kHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
) 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
Buoy
A buoy is a floating device that can have many different purposes. It can be anchored or allowed to drift. The word, of Old French or Middle Dutch origin, is now most commonly in UK English, although some orthoepists have traditionally prescribed the pronunciation...
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
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
/ radar.
Due to the low frequency, a VLF broadcast antenna needs to be quite big. In fact, broadcasting sites are usually a few square kilometers (or miles). This of course 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 surface and communicate on other, higher, frequencies (such as UHF or VHF).
This band allows for a roughly 300 bit/s transmission - or about 35 8-bit ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
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 results in a baud rate (characters per second) increase of 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
Extremely low frequency
Extremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...
frequency range (3–30 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
) (see also SLF
Super low frequency
Super-low frequency is the frequency range between 30 hertz and 300 hertz. This frequency range includes the frequencies of AC power grids ....
) can travel through the oceans and reach submarines anywhere. Building an ELF transmitter is a formidable challenge, as they have to work at incredibly long wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s: The US Navy's system (called Seafarer
Sanguine (transmitter)
Sanguine was the name of an SLF-transmitter of the US-Navy, which was used to transmit on the frequency 76 hertz signals to submarines. The transmitter sites were in Michigan and Wisconsin. As aerial ground dipoles were used....
) operated at 76 hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, the Soviet/Russian system (called ZEVS
ZEVS
Zevs or ZEVS may refer to:* ZEVS, A Soviet/Russian submarine communication system, see Communication with submarines.* Zevs, A French street artist, see Zevs...
) at 82 hertz. The latter corresponds to a wavelength of 3658.5 kilometers. That is more than a quarter of the Earth's diameter. Obviously, the usual half-wavelength dipole antenna
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
cannot be constructed, as it would spread across a large country.
Instead, one has to find an area with very low ground conductivity
Ground conductivity
Ground conductivity refers to the electrical conductivity of the subsurface of the earth.-Radio propagation:Ground conductivity is an extremely important factor in determining the field strength and propagation of surface wave radio transmissions...
(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
Murmansk
Murmansk is a city and the administrative center of Murmansk Oblast, Russia. It serves as a seaport and is located in the extreme northwest part of Russia, on the Kola Bay, from the Barents Sea on the northern shore of the Kola Peninsula, not far from Russia's borders with Norway and Finland...
. 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 52 kilometres (32.3 mi). 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 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s. Its transmission can be received virtually anywhere. A station in Antarctica at 78°S 167°W noticed when the Soviet Navy put their ZEVS antenna into operation.
Due to the technical difficulty of building an ELF transmitter, only the USA 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
Clam Lake, Wisconsin
Clam Lake is an unincorporated, census-designated place in the town of Gordon in Ashland County, Wisconsin, United States. It is located on Wisconsin Highway 77 near County Highway GG...
(since 1977) and at Republic, Michigan in the Upper Peninsula (since 1980). Before 1977, the Sanguine system was used, placed in the Laurentian Shield in Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
. The Russian antenna (ZEVS, 82 Hz) is installed at the Kola Peninsula
Kola Peninsula
The Kola Peninsula is a peninsula in the far northwest of Russia. Constituting the bulk of the territory of Murmansk Oblast, it lies almost completely to the north of the Arctic Circle and is washed by the Barents Sea in the north and the White Sea in the east and southeast...
near Murmansk. It was noticed in the West in the early 1990s. The British Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
once considered building their own transmitter at Glengarry
Invergarry
Invergarry is a village in the Highlands of Scotland. It is in the Great Glen, near where the River Garry flows into Loch Oich.Near the centre of the village is the junction between the A82 road and the A87 road which branches off to the west towards Skye.The ruined Invergarry Castle is situated...
Forest, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, 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 ratioSignal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
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
Spoofing attack
In the context of network security, a spoofing attack is a situation in which one person or program successfully masquerades as another by falsifying data and thereby gaining an illegitimate advantage.- Spoofing and TCP/IP :...
).
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 HFHigh frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
, VHF and UHF voice and teleprinter circuits. Where available, dedicated military communications satellite
Communications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
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).
See also
- TACAMOTACAMOTACAMO is a U.S. military term meaning "Take Charge and Move Out". TACAMO refers to a system of survivable communications links designed to be used in nuclear war to maintain communications between the decision makers and the triad of strategic nuclear weapon delivery systems...
, radio system intended to survive nuclear attack - Extremely low frequencyExtremely low frequencyExtremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...
- Super low frequencySuper low frequencySuper-low frequency is the frequency range between 30 hertz and 300 hertz. This frequency range includes the frequencies of AC power grids ....
- Radio for Underwater Communications
External links
- Radio Communications of German U-boats in WWI and WWII
- About the U.S. ELF projects
- ZEVS, The Russian 82 Hz ELF Transmitter By Trond Jacobsen at ALFLAB, Halden in Norway
- Extremely Low Frequency Transmitter Site Clam Lake, Wisconsin, a "Fact File" published by the US Navy (PDF File)
- Military Communications by Christopher H. Sterling