Call sign

In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity.

The use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose. This pattern continued in radiotelegraph operation; radio companies initially assigned two-letter identifiers to coastal stations and stations aboard ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi Station) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country.

Ships and boats

Russian Nuclear Icebreaker "Arktika" with call sign UKTY

One of the earliest applications of radiotelegraph operation, long predating broadcast radio, were marine radio stations installed aboard ships at sea. In the absence of international standards, early transmitters constructed after Guglielmo Marconi's first trans-Atlantic message in 1901 were issued arbitrary two-letter calls by radio companies, alone or later preceded by a one-letter company identifier. These mimicked an earlier railroad telegraph convention where short, two-letter identifiers served as Morse code abbreviations to denote the various individual stations on the line (for instance, AX could represent Halifax). 'N' and two letters would identify US Navy; 'M' and two letters would be a Marconi Station. On April 14, 1912, the RMS Titanic station MGY, busily delivering telegram traffic from ship's passengers to the coastal station at Cape Race, Newfoundland (call sign MCE), would receive warnings of ice fields from Marconi stations aboard the M.V. Mesaba (call sign MMU) and the S.S. Californian (call sign MWL). Its distress call CQD CQD CQD CQD CQD CQD DE MGY MGY MGY MGY MGY MGY position 41.44N 50.24W would be answered by a station aboard the Carpathia (call sign MPA). Later that same year, an international conference standardised radio call signs so that the first two letters would uniquely identify a transmitter's country of origin.

Merchant and naval vessels are assigned call signs by their national licensing authorities. In the case of states such as Liberia or Panama, which are flags of convenience for ship registration, call signs for larger vessels consist of the national prefix plus three letters (for example, 3LXY, and sometimes followed by a number, i.e. 3LXY2). United States merchant vessels are given call signs beginning with the letters "W" or "K" while US naval ships are assigned callsigns beginning with "N". Originally both ships and broadcast stations were given call signs in this series consisting of three or four letters, but as demand for both marine radio and broadcast call signs grew, gradually American-flagged vessels were given longer call signs with mixed letters and numbers.

As broadcast stations became commonplace in the 1920s, some original three and four-letter call signs were reassigned as the corresponding ships were removed from U.S. registry. The WSB call sign had been held by two ships (the SS Francis H. Leggett, shipwrecked off Oregon's coast on September 18, 1914, and later the Firwood, a ship destroyed by fire near Peru on December 18, 1919) before being assigned to the Atlanta Journal for use by its presumably unsinkable Atlanta, Georgia broadcast radio station in 1922. Similarly WEZU, the international radio call sign of the ship SS Lash Atlantico, was assigned in 1997 to a broadcast station. Additional call signs would be reassigned to coastal stations or moved from marine radio to terrestrial broadcast radio when ships were sold for registration to foreign nations, as the new owners would obtain new, local call signs for any existing shipboard radio stations.

Leisure craft with VHF radios may not be assigned call signs, in which case the name of the vessel is used instead. Ships in the US wishing to have a radio licence anyway are under F.C.C. class SA: "Ship recreational or voluntarily equipped." Those calls follow the land mobile format of the initial letter K or W followed by 1 or 2 letters followed by 3 or 4 numbers (such as KX0983 or WXX0029).

U.S. Coast Guard small boats have a number that is shown on both bows (i.e. port and starboard) in which the first two digits indicate the nominal length of the boat in feet. For example, Coast Guard 47021 refers to the 21st in the series of 47 foot motor lifeboats. The call sign might be abbreviated to the final two or three numbers during operations, for example: Coast Guard zero two one.

Aviation

A general aviation aircraft in the United States with its FAA civilian registration number (N98710), which also doubles as its call sign, displayed on the fuselage. However, since this is a Civil Air Patrol aircraft, it will generally be identified by CAPxxxx, based on the state from which it hails.

Call signs in aviation are derived from several different policies, depending upon the type of flight operation and whether or not the caller is in an aircraft or at a ground facility. In most countries, unscheduled general aviation flights identify themselves using the call sign corresponding to the aircraft's registration number (also called N-number in the U.S., or tail number). In this case, the call sign is spoken using the International Civil Aviation Organization (ICAO) phonetic alphabet. Aircraft registration numbers internationally follow the pattern of a country prefix, followed by a unique identifier made up of letters and numbers. For example, an aircraft registered as N978CP conducting a general aviation flight would use the call sign November-niner-seven-eight-Charlie-Papa. However, in the United States a pilot of an aircraft would normally omit saying November, and instead use the name of the aircraft manufacturer or the specific model. At times, general aviation pilots might omit additional preceding numbers and use only the last three numbers and letters. This is especially true at uncontrolled fields (those without control towers) when reporting traffic pattern positions, or at towered airports after establishing two-way communication with the tower controller. For example, Skyhawk eight-Charlie-Papa, left base (see below).

In most countries, the aircraft call sign or "tail number"/"tail letters" (also known as registration marks) are linked to the international radio call sign allocation table and follow a convention that aircraft radio stations (and, by extension, the aircraft itself) receive call signs consisting of five letters. For example, all British civil aircraft have a five-letter call sign beginning with the letter G. Canadian aircraft have a call sign beginning with C–F or C–G, such as C–FABC. Wing In Ground-effect vehicles (hovercraft) in Canada are eligible to receive C–Hxxx call signs, and ultralight aircraft receive C-Ixxx call signs. In days gone by, even American aircraft used five letter call signs, such as KH–ABC, but they were replaced prior to World War II by the current American system of civilian aircraft call signs (see below).

The dash ("-") in the registration is only included on the fuselage of the airplane for readability. In air traffic management systems (ATC radar screen, flow management systems, etc.) and on flight plan forms, the dash is not used (e.g. PHVHA, FABCD, CFABC).

After an aircraft has made contact with an air traffic control facility, the call sign may be abbreviated. Sometimes the aircraft make or model is used in front of the full or abbreviated call sign, for instance, the American aircraft mentioned above might then use Cessna Eight-Charlie-Papa. Alternatively, the initial letter of the call sign can be concatenated with the final two or three characters, for instance a British aircraft registered G–BFRM may identify as Golf–Romeo–Mike while the American aircraft might use November–Eight-Charlie-Papa. The use of abbreviated call signs has its dangers, in the case when aircraft with similar call signs are in the same vicinity. Therefore, abbreviated signs are used only so long as it is unambiguous.

The United States does not follow the five-letter call sign convention, and in that country the registration number begins with the letter N followed by up to five digits and/or letters in one of these schemes: one to five numbers (N12345), one to four numbers and one suffix letter (N1234Z), or one to three numbers and two suffix letters (N123AZ). The numeric part of the registration never starts with zero.

Commercial operators, including scheduled airline, air cargo and air taxi operators, will usually use an ICAO or FAA-registered call sign for their company. By ICAO Annex 10 Chapter 5.2.1.7.2.1 - Full call signs type C, a call sign consists out of the telephony designator of the aircraft operating agency, followed by the flight identification. The flight identification is very often the same as the flight number, but could be different due to call sign confusion, if two or more flights close to each other have similar flight numbers (i.e. KLM649 and KLM645 or BAW466 and BAW646). For example, British Airways flight 75 would use the call sign Speedbird Seven–Five, since Speedbird is the telephony designator for British Airways and 75 would be the flight identification. (The telephony designator is not the same as the call sign, although the two are sometimes conflated). Pan Am had the telephony designator of Clipper. (see list)

For these call signs, proper usage varies by country. In some countries, such as the United States, numbers are spoken normally (for the example above, Speedbird Seventy-five) instead of being spelled out digit by digit, leading to the possibility of confusion. In most other countries, including the United Kingdom, they are spelled out. Air taxi operators in the United States sometimes do not have a registered call sign, in which case the prefix T is used, followed by the aircraft registration number (e.g. Tango- November-Niner-Seven-Eight-Charlie-Papa).

Some variations of call signs exist to express safety concerns to all operators and controllers monitoring the transmissions. Aircraft call signs will use the suffix "heavy" for heavy aircraft, to indicate an aircraft that is going to cause significant wake turbulence, e.g. United Two-Five Heavy; All aircraft capable of operating with a gross take-off weight of more than 300,000 lbs. must use this suffix whether or not they are operating at this weight during a particular phase of flight. These are typically Boeing 747, some models of the 757, 777, or 767, Airbus A340, A330 and A300, McDonnell Douglas DC-10 or MD-11, or Lockheed L-1011 aircraft. The suffix "super" is used for the Airbus A380. For air ambulance services or other flights involving the safety of life (such as aircraft carrying a person who has suffered a heart attack), "lifeguard" is added to the call sign. For flights in which life is not in direct danger (such as transporting organs for transplant), the call sign prefix "Pan-Pan-Medical" is used before the normal call sign, e.g. Pan-Pan-Medical Three-Three-Alpha, Pan-Pan-Medical Northwest Four-Five-Eight, or Pan-Pan-Medical Singapore Niner-Two-Three. Pan Pan (pronounced "pahn-pahn") is the voice radio signal for "urgent", while Mayday is the voice radio signal for "distress". The word may be omitted for air ambulance services with assigned call signs, especially when they have notified air traffic control operators that they are on an air ambulance mission at the beginning of their flight and do not change from one controller to another. The Life Flight air ambulance service, for example, might simply identify as Life-Flight Three. An aircraft that has declared an in-flight emergency will sometimes prefix the word Mayday to its call sign.

Formerly one of the rarest call signs, "Concorde", was once used to identify British Airways Concorde aircraft. The intent of this call sign was to raise the air traffic control operators' awareness of the unique performance of the aircraft and the special attention it required. The call sign was appended to British Airways' normal radio call sign, e.g. "Speedbird-Concorde One". In normal service, Air France did not use it at all; its Concorde flights simply used the standard Airfrans call sign.

Glider pilots often can use any of three different call signs. Since most (not all) gliders now show standard CAA general aviation registrations e.g. G-xxxx they can call using the same call sign and abbreviation rules as other light aircraft. This has long been in the case in the United States. Before these registrations came in (between 2004 and 2008) they used to use and normally still do use either a three letter code issued to all gliders by the British Gliding Association known as the aircraft's Trigraph e.g. XYZ normally calling ATC as "Glider X-ray, Yankee, Zulu" or if they paid extra could get from the BGA a numeric or mixed numeric and letter code known as a competition number for marking their aircraft and as a call sign. For Example R4 "Romeo Four", or 26 "Two Six" or F1 "Foxtrot One". Optionally gliders will normally tag on the "Glider" in front of their call sign when calling ATC units so that the controller knows for example that the glider will be unable to maintain a particular height as Gliders are normally either descending in a straight glide or circling to climb. Some gliders are still not required to carry a CAA General Aviation type registration as they are older designs or prototypes and can therefore only continue to just use their Trigraph or Competition number as a call sign. These are known as Annex II aircraft as they are listed in EASA Annex II.

Military flights often use more than one call sign during a flight. Administrative call signs are used with air traffic control facilities similar to those of commercial operators. e.g. Navy Alpha-Golf-Two-One, Reach-Three-One-Seven-Niner Two.

Tactical call signs are used during tactical portions of a flight, and they often indicate the mission of the flight and/or an aircraft's position in a formation.

For example, Canadian Air Force 442 Rescue Squadron, based at Comox, British Columbia uses the call sign "Snake 90x" depending on the tail number of the helicopter: 901, 902, etc. When tasked on a search and rescue (SAR) mission, however, the aircraft call sign becomes "Rescue 90x".

Ground facilities identify themselves by the name and function of the facility: e.g. Seattle Tower for the tower air traffic control operators' position, SoCal Approach for a TRACON, or Boston Center for an Area Control Center. All other ICAO countries around the world, for example the European Joint Aviation Authorities (JAA), use Control or Radar instead of Center in their airspace. (Langen Radar, Brussels Control, Paris Control, ...). London Centre (center) is the emergency frequency call sign for London Terminal Control TC.

The ICAO 24–bit transponder code is intended for non-human usage in the Mode-S and ADS-B protocols.

FAA aircraft identification regulations

The Federal Aviation Administration regulates call sign standards within United States airspace. These conventions are generally used worldwide.

position	call sign	comments
President of the United States	Air Force One	any US Air Force aircraft when the President is aboard, typically VC-25A aircraft, Air Force One Foxtrot when only the family of the President is aboard.
President of the United States	Marine One	any US Marine Corps aircraft when the President is aboard, typically VH-60N or VH-3D Sea King helicopters, Marine One Foxtrot when only the family of the President is aboard.
President of the United States	Navy One	any US Navy aircraft when the President is aboard; to date, this call sign has been used only once
President of the United States	Executive One	any civilian aircraft when the President is aboard, Executive One Foxtrot when only the family of the President is aboard.
Vice President of the United States	Air Force Two	any US Air Force aircraft when the Vice President is aboard
Vice President of the United States	Marine Two	any US Marine Corps aircraft when the Vice President is aboard
Vice President of the United States	Coast Guard Two	any US Coast Guard aircraft when the Vice President is aboard; to date, this call sign has been used only once.
United States Secretary of Transportation	Transport One	any aircraft when the secretary is aboard, Transport Two when the Deputy Secretary of Transportation is aboard
Administrator of the Federal Aviation Administration	Safe Air One	any aircraft when the Administrator is aboard, Safe Air Two when the Deputy Administrator
United States Department of Energy	RAC followed by tail number	any Department of Energy Flight
	FLIGHT CHECK followed by tail number	any FAA flight testing navigational aids
	SAMP followed by tail number	any United States Air Force aircraft conducting air sampling

Spacecraft

Radio call signs used for communication in manned spaceflight is not formalized or regulated to the same degree as for aircraft. The three nations currently launching manned space missions use different methods to identify the ground and space radio stations; the United States uses either the names given to the space vehicles, or else the project name and mission number. Russia traditionally assigns code names as call signs to individual cosmonauts, more in the manner of aviator call signs, rather than to the spacecraft.

The only continuity in call signs for spacecraft have been the issuance of "ISS"-suffixed call signs by various countries in the Amateur Radio service as a citizen of their country has been assigned there. The first Amateur Radio call sign assigned to the International Space Station was NA1SS by the United States. OR4ISS (Denmark), DP0ISS (Germany), and RS0ISS (Russia) are examples of others, but are not all-inclusive of others also issued.

United States

In America's first manned space program Project Mercury, the astronauts named their individual spacecraft. These names each consisted of a significant word followed by the number 7 (representing the seven original astronauts), and were used as the call signs by the capsule communicators (CAPCOMs).

Flight	Astronaut	Call sign
Mercury-Redstone 3	Alan Shepard	Freedom 7
Mercury-Redstone 4	Gus Grissom	Liberty Bell 7
Mercury-Atlas 6	John Glenn	Friendship 7
Mercury-Atlas 7	Scott Carpenter	Aurora 7
Mercury-Atlas 8	Wally Schirra	Sigma 7
Mercury-Atlas 9	Gordon Cooper	Faith 7

In Project Gemini, the astronauts were not officially permitted to name their two-man spacecraft, which was identified by "Gemini" followed by the mission number (3 through 12). A notable exception was that Gus Grissom named his Gemini 3 spacecraft Molly Brown after the Titanic survivor, as a joke based on his experience with his Liberty Bell 7 capsule sinking. This name was used as a call sign by CAPCOM L. Gordon Cooper, without NASA's approval.

Starting with the second flight Gemini 4, NASA used the Lyndon B. Johnson Space Center to house the flight control center, and its call sign was Houston, chosen for its location. This practice continues to this day.

The practice of using the mission number continued through the first two flights of the Project Apollo manned lunar landing program, Apollo 7 and Apollo 8. But all remaining Apollo missions included two manned spacecraft (Command/Service Module (CSM) and Lunar Module (LM)) on each flight, which required the use of separate call signs for each vehicle when they flew independently of each other. For this reason, NASA permitted the three-man crews to name both craft for each of their missions, and these names were used as the call signs. A temporary exception to this was on the first Moon landing, Apollo 11: since the first Moon landing site was in the Sea of Tranquillity, the call sign Tranquillity Base was used while the LM was on the lunar surface. Before and after independent flight of the LM, the mission number was used as the call sign. The Apollo call signs were:

Flight	Command Module	Lunar Module
Apollo 9	Gumdrop	Spider
Apollo 10	Charlie Brown	Snoopy
Apollo 11	Columbia	Eagle
Apollo 12	Yankee Clipper	Intrepid
Apollo 13	Odyssey	Aquarius
Apollo 14	Kitty Hawk	Antares
Apollo 15	Endeavour	Falcon
Apollo 16	Casper	Orion
Apollo 17	America	Challenger

For project Skylab, the practice returned to using the mission name as the spacecraft call sign, since the Skylab station was always unmanned while the shuttle vehicle (an Apollo CSM) carried a crew to it or back to Earth.

The six Space Shuttle orbiters were given individual names (they also had letter-and-number callsigns) by NASA, which were used as the call signs: Enterprise (OV-101, which was not fitted for spaceflight), Columbia (OV-102), Challenger (OV-099), Discovery (OV-103), Atlantis (OV-104), and Endeavour (OV-105). Of these, Columbia, Challenger, and Endeavour had previously served as call-signs of Apollo spacecraft.

Russia (including former Soviet Union)

Main article: Soviet spacecraft call signs

The first man in space, Yuri Gagarin, was given the call sign Kedr ("cedar" in Russian) aboard Vostok 1, and the first woman, Valentina Tereshkova, was Chaika ("Seagull") on Vostok 6. Flight control used the call sign Zarya, meaning "dawn".

When the Voskhod multi-pilot spacecraft flew, the call sign was assigned to the command pilot, and this was suffixed with the number 2 or 3 to designate subordinate crew members by rank. On Voskhod 1, command pilot Vladimir Komarov was Ruby 1, flight engineer Konstantin Feoktistov was Ruby 2, and medical doctor Boris Yegorov was Ruby 3. On Voskhod 2, command pilot Pavel Belyayev was Diamond 1, and Alexey Leonov, the first man to walk in space, was Diamond 2.

International Space Station

The call sign of the International Space Station was Alpha, now Station.

Amateur radio

Further information: ITU prefix - amateur and experimental stations

Some U.S. states issue call sign license plates for motor vehicles owned by amateur radio operators.

Amateur radio call signs are in the international series and normally consist of a one or two character prefix, a digit (which may be used to denote a geographical area, class of license, or identify a licensee as a visitor or temporary resident), and a 1, 2, or 3 letter suffix. In Australia call signs are structured with a two letter prefix, a digit (which identifies geographical area), and a 2, 3 or 4 letter suffix. This suffix may be followed by a further suffix, or personal identifier, such as /P (portable), /M (mobile), /AM (aeronautical mobile) or /MM (maritime mobile). The number following the prefix is normally a single number (0 to 9). Some prefixes, such as Djibouti's (J2), consist of a letter followed by a number. Hence, in the hypothetical Djibouti call sign, J29DBA, the prefix is J2, the number is 9, and the suffix is DBA. Others may start with a number followed by a letter, for example, Jamaican call signs begin with 6Y. When operating with reciprocal agreements under the jurisdiction of a foreign government, an identifying station pre-pends the call sign with the country prefix and number of the country/territory from which the operation is occurring. For example, W4/G3ABC would denote a licensed amateur from the United Kingdom who is operating in the fourth district of the United States. There are exceptions; in the case of U.S./Canadian reciprocal operations, the country/territory identifier is, instead, appended to the call sign; e.g., W1AW/VE4, or VE3XYZ/W1.

Occasionally, special call signs are issued in the amateur radio service either for special purposes, VIPs, or for temporary use to commemorate special events. Examples include VO1S (VO1 as a Dominion of Newfoundland call sign prefix, S to commemorate Marconi's first trans-Atlantic message, a single-character Morse code S sent from Cornwall, England to Signal Hill, St. John's in 1901) and GB90MGY (GB as a Great Britain call sign prefix, 90 and MGY to commemorate the 90th anniversary of historic 1912 radio distress calls from MGY, the Marconi station aboard the famed White Star luxury liner RMS Titanic).

The late King Hussein of Jordan was issued a special amateur license number, JY1, which would have been the shortest possible call sign issued by the Hashemite Kingdom of Jordan.

When identifying a station by voice, the call sign may be given by simply stating the letters and numbers, or using a phonetic alphabet. Some countries mandate the use of the phonetic alphabet for identification.

Broadcast call signs

While broadcast radio stations will often brand themselves with plain-text names, identities such as "cool FM", "rock 105" or "the ABC network" are not globally unique. Another station in another city or country may (and often will) have a similar brand; the name of a broadcast station for legal purposes is therefore normally its ITU call sign.

North America

Main article: Call signs in North America

See also: List of radio stations in North America by media market

Broadcast stations in North America generally use call signs in the international series. There are some common conventions followed in each country. In the United States, the first letter generally is K for stations west of the Mississippi River and W for those east of the Mississippi; all new call signs have been 4-character for some decades, though there are historical 3-character call letters still in use today, such as KSL in Salt Lake City and WGN in Chicago.

There are a number of exceptions to the east/west rule, such as KDKA in Pittsburgh and WFAA in Dallas-Fort Worth, but these are historical artifacts from a rule change in the 1920s, and most of the exceptions are located in the states immediately to either side of the river, in the state of Louisiana in the metropolitan areas of Baton Rouge and Greater New Orleans, and markets north of the river's source such as Fargo–Moorhead and Duluth–Superior. The westernmost station in the continental United States beginning with W is WOAI in San Antonio. WVUV-LP in Pago Pago, American Samoa, was the westernmost station with a W call sign until 2008. KYW in Philadelphia (which originated in Chicago in 1921, moved to Philadelphia in 1934, and existed in Cleveland in the late 1950s/early 1960s) is now the easternmost station with a K call sign.

A 1940 QSL card for WWV, indicating its early location in the U.S. state of Maryland.

Another exception to this is that all time-broadcasting stations have a three or four letter call sign beginning with WWV. The three current government-operated time stations, WWV (and longwave sister station WWVB), and WWVH, are located in Fort Collins, Colorado and Kekaha, Hawaii, respectively, both of which would normally use call signs beginning with "K".

The US government-operated international broadcaster the Voice of America no longer has call signs assigned to it; however, Radio Canada International's transmitter in Sackville, NB is still assigned CKCX. Privately operated shortwave stations, like WWCR and CFRX, also have call signs.

In Canada, the publicly owned Canadian Broadcasting Corporation uses CBC Radio; privately owned commercial broadcast stations use primarily CF and CH through CK prefixes; and four stations licensed to St. John's by the Dominion of Newfoundland government retain their original VO calls.

In Mexico, AM radio stations use XE call signs (such as XEW-AM), while the majority of FM radio and television stations use XH. Broadcast call signs are normally four or five alpha characters in length, plus the -FM or -TV suffix where applicable.

Oceania

Main article: Call signs in Oceania

Call signs are allocated by the Australian Communications and Media Authority and are unique for each broadcast station. The use of call signs on-air in both radio and television in Australia is optional, so many stations used other on-air identifications. Call signs are no longer used in New Zealand, but historically call signs consisted of a number, an X, Y, or Z, and another letter (e.g. 1YA).

Asia

Main article: Call signs in Asia

Most Asian countries do not use call signs to identify broadcast stations, instead using other methods. However, Japan, South Korea, Indonesia, the Philippines and Taiwan do have call sign systems.

Europe

Main article: Call signs in Europe

In Europe, call signs are normally not used for broadcast stations. TV and radio stations have unique names and abbreviations. Britain has no call signs in the American sense, but allow broadcast stations to choose their own trade mark call sign up to six words in length.

South America

Main article: Call signs in South America

In South America call signs have been a traditional way of identifying radio and TV stations. Some stations still broadcast their call signs a few times a day, but this practice is becoming very rare. Argentinian broadcast call signs consist of two or three letters followed by multiple numbers, the second and third letters indicating region. In Brazil, radio and TV stations are identified by a ZY, a third letter and three numbers. ZYA and ZYB are allocated to television stations, ZYI, ZYJ, ZYL and ZYK designate AM stations, ZYG is used for shortwave stations, ZYC, ZYD, ZYM and ZYU are given to FM stations.

Military call signs

In wartime, monitoring an adversary's communications can be a valuable form of intelligence. Consistent call signs can aid in this monitoring, so in wartime, military units often employ tactical call signs and sometimes change them at regular intervals. In peacetime, some military stations will use fixed call signs in the international series.

U.S. Army

The United States Army uses fixed station call signs which begin with W, such as WAR, used by U.S. Army Headquarters.

Tactical call signs are often assigned to a company sized unit or higher. For example, the collective "Checkmate" might be assigned to an entire company and thus "Checkmate 1 Actual" would be the first platoon leader, "Checkmate 2 Actual" to the second platoon leader, etc. "Checkmate Actual" is the Company Commander and "Checkmate" is the captain's radio-telephone operator (or other designee, such as the XO). This system can be extended to squad or fireteam level by adding another number, for example the squad leader of the second squad of the third platoon in Checkmate company would have the call sign "Checkmate 32", pronounced "three-two". Additionally, only the squad leader proper will answer to the call sign "Checkmate 32 Actual", whereas the squad leader's radio-telephone operator (or other designee) will answer to the call sign "Checkmate 32" (without the "Actual") as a matter of routine. Also, companies often have the letter they are designated by ('A', 'B', 'C' or 'D') be the first letter of their call sign. This means a 'C' Company could potentially have 'Checkmate' as its call sign.

U.S. Air Force

Fixed call signs for the United States Air Force stations begin with A, such as AIR, used by USAF Headquarters. The USAF also uses semi-fixed identifiers consisting of a name followed by a two or three digit number. The name is assigned to a unit on a semi-permanent basis; they change only when the U.S. Department of Defense goes to DEFCON 3. For example, JAMBO 51 would be assigned to a particular B-52 aircrew of the 5th Bomb Wing, while NODAK 1 would be an F-16 fighter with the North Dakota Air National Guard.

The most recognizable call sign of this type is Air Force One, used when any Air Force aircraft is transporting the U.S. President. Similarly, when the President is flown in a U.S. Marine Corps helicopter, the call sign is Marine One. When then-president George W. Bush, a former Air National Guard fighter pilot, was flown to the aircraft carrier USS Abraham Lincoln in a Navy S-3B Viking, it was the first use of the "Navy One" call sign.

Individual military pilots or other flight officers usually adopt a personal aviator call sign.

U.S. Navy/U.S. Marine Corps/U.S. Coast Guard

The United States Navy, United States Marine Corps, and United States Coast Guard use a mixture of tactical call signs and international call signs beginning with the letter N. For example, the carrier USS John F. Kennedy had the call sign NJFK for unclassified and navigation communications with other vessels, but uses tactical call signs that vary with its mission. In tactical situations, the Marine Corps utilizes call signs naming conventions similar to the Army's.

British Army

Tactical voice communications ("combat net radio") use a system of call signs of the form letter-digit-digit. Within a standard infantry battalion these characters represent companies, platoons and sections respectively, so that 3 Section, 1 Platoon of B Company might be F13. In addition, a suffix following the initial call sign can denote a specific individual or grouping within the designated call sign, so F13C would be the Charlie fire team. Unused suffixes can be used for other call signs that do not fall into the standard call sign matrix, for example the unused 33A call sign is used to refer to the Company Sergeant Major.

Note that the letter part of the call sign is not the company's own letter (B vs F in the above example) - indeed, the letter designations are randomly assigned using BATCO sheets, and appear on CEIs (communication electronic instructions), and change along with the BATCO codes every 24 hours. This, together with frequency changes and voice procedure aimed at making every unit sound the same, introduces a degree of protection against simple traffic analysis and eavesdropping.

Not all radio users fit into the standard battalion model, but in order to continue the obfuscation they will be assigned a call sign that appears to be part of such a system. Presumably, the well-known B20 falls into this category.

Finally, the controller of each net has the call sign 0 ("zero"). There may also be a second controller - either a backup station or a commander who has delegated communication tasks to a signaller but may occasionally wish to speak in person - using the call sign 0A ("zero alpha").

Appointment titles

Earlier systems used a series of appointment titles to identify users and individuals, "Sunray", for instance, referring to the appropriate leader. Titles such as "Sunray" and (Sunray) Minor are still used. There are several appointment titles, such as "Ironside" which are no longer used by the British Army. Several other armed forces still use appointment titles, including the Australian and Canadian army.

Ser	Appointment	Title
1	Commander (Battalion, Company, Platoon)	SUNRAY
2	Second-in-command	SUNRAY MINOR
3	Adjutant	SEAGULL
4	Intelligence Officer	ACORN
5	Quartermaster	MOLAR
6	Armour	IRONSIDE
7	Artillery	SHELLDRAKE
8	Engineer	HOLDFAST
9	Signals	PRONTO
10	Infantry	FOXHOUND
11	Medical Rep	STARLIGHT

Due to the predictable nature of some of these, such as "SHELLDRAKE", all but SUNRAY and MINOR were removed from use in the British Army.

Transmitters requiring no call signs

No call signs are issued to transmitters of long-range navigation systems (Decca, Alpha, Omega), or transmitters on frequencies below 10 kHz, because frequencies below 10 kHz are not subject to international regulations. In addition, in some countries lawful unlicensed low-power personal and broadcast radio signals (Citizen's Band, Part 15 or ISM bands) are permitted; an international call sign is not issued to such stations due to their unlicensed nature. Also, wireless network routers or mobile devices and computers using Wi-Fi are unlicensed and do not have call signs. On some personal radio services, such as Citizen's Band it is considered a matter of etiquette to create one's own call sign, which is called a handle (or trail name). Some wireless networking protocols also allow an SSID to be set as an identifier, but with no guarantee that this label will remain unique.

International regulations no longer require a call sign for broadcast stations; however, they are still required for broadcasters in many countries, including the United States. Mobile phone services do not use call signs on-air for obvious reasons ; however, the U.S. still assigns a call sign to each mobile-phone spectrum license.

In the United States, voluntary ships operating domestically are not required to have a call sign or license to operate VHF radios, radar or a distress radiobeacon. Voluntary ships (mostly pleasure and recreational) are not required to have a radio. However ships which are required to have radio equipment (most large commercial vessels) are issued a call sign.

See also

• Airline call sign
• ITU prefix - amateur and experimental stations
• Callbook
• Cosmonaut call sign
• Maritime Mobile Service Identity
• Pseudonym
• Station identification
• Procedure word
• NATO phonetic alphabet
• Pan-pan

Further reading

• United States Federal Aviation Administration, Aeronautical Information Manual, Official Guide to Basic Flight Information and ATC Procedures, 2004. Chapter 4, Section 2

External links

• United States Call Sign Policies
• United States "FCC" call sign search
• FCC amateur radio operator search
• Amateur Call Prefixes
• Internet Radio uniform call sign program
• Military Call Sign Database
• Military Call Sign List
• Another Military Callsign List
• Fictional Story About Military Call Signs
• Radio-Locator a search engine of all of the radio stations in the world with websites, searchable by location, frequency, and call sign
• Broadcasting undertaking callsigns possibly available for assignment - Industry Canada