The NATO phonetic alphabet, more formally the international radiotelephony spelling alphabet, is the most widely used spelling alphabet. Though often called "phonetic alphabets", spelling alphabets have no connection to phonetic transcription systems like the International Phonetic Alphabet. Instead, the NATO alphabet assigns code words to the letters of the English alphabet acrophonically so that critical combinations of letters (and numbers) can be pronounced and understood by those who transmit and receive voice messages by radio or telephone regardless of their native language, especially when the safety of navigation or persons is essential. The paramount reason is to ensure intelligibility of voice signals over radio links. It is used by many national and international organizations, including the International Civil Aviation Organization (ICAO), the International Telecommunication Union (ITU), the International Maritime Organization (IMO), the North Atlantic Treaty Organisation (NATO), the Federal Aviation Administration (FAA), and the American National Standards Institute (ANSI). It is a subset of the much older International Code of Signals (INTERCO), which originally included visual signals by flags or flashing light, sound signals by whistle, siren, foghorn, or bell, as well as one, two, or three letter codes for many phrases. However, ATP-1 is marked NATO Confidential (or the lower NATO Restricted) so it is not publicly available. Nevertheless, a NATO unclassified version of the document is provided to foreign, even hostile, militaries, even though they are not allowed to make it publicly available.

Alphabet and pronunciation
The first internationally recognized alphabet was adopted by the ITU in 1927. The experience gained with that alphabet resulted in several changes being made in 1932 by the ITU. The resulting alphabet was adopted by the International Commission for Air Navigation, the predecessor of the ICAO, and was used in civil aviation until World War II. It continued to be used by the IMO until 1965:
Amsterdam Baltimore Casablanca Denmark Edison Florida Gallipoli Havana Italia Jerusalem Kilogramme Liverpool Madagascar New_York Oslo Paris Quebec Roma Santiago Tripoli Upsala Valencia Washington Xanthippe Yokohama Zurich
During World War II (specifically in 1941), the requirements of joint Allied operations led to the development of the Joint Army/Navy Phonetic Alphabet:
Able Baker Charlie Dog Easy Fox George How Item Jig King Love Mike Nan Oboe Peter Queen Roger Sugar Tare Uncle Victor William X-ray Yoke Zebra
Several RAF phonetic alphabets were also used. After the war, with many aircraft and ground personnel drawn from the allied armed forces, "Able Baker" continued to be used in civil aviation. But many sounds were unique to English, so an alternative "Ana Brazil" alphabet was used in Latin America. But the International Air Transport Association (IATA), recognizing the need for a single universal alphabet, presented a draft alphabet to the ICAO in 1947 which had sounds common to English, French, and Spanish. After further study and modification by each approving body, the revised alphabet was implemented November 1, 1951:
Alfa Bravo Coca Delta Echo Foxtrot Golf Hotel India Juliett Kilo Lima Metro Nectar Oscar Papa Quebec Romeo Sierra Tango Union Victor Whisky Extra Yankee Zulu
Immediately, problems were found with this list—some users felt they were so severe that they reverted to the old "Able Baker" alphabet. To identify the deficiencies of the new alphabet, testing was conducted among speakers from 31 nations, principally by the governments of the United Kingdom and the United States. Confusion among words like Delta, Nectar, Victor, and Extra, or omission of other words under poor receiving conditions were the main problems. After much study, only five words representing the letters C, M, N, U, and X were replaced. The final version given in the table above was implemented by the ICAO on March 1, 1956, Because the ITU governs all international radio communications, it was also adopted by all radio operators, whether military, civilian, or amateur (ARRL). It was finally adopted by the IMO in 1965. In 1947 the ITU adopted the compound number words (Nadazero Unaone, etc.), later adopted by the IMO in 1965.

History
The alphabet is used to spell out parts of a message or call sign that are critical or otherwise hard to recognize during voice communication. For instance the message "proceed to map grid DH98" could be transmitted as "proceed to map grid Delta-Hotel-Niner-Eight" and a C-130 Hercules plane directly ahead might be described as a "Charlie One Three Zero in your twelve o'clock". Several letter codes and abbreviations using the phonetic alphabet have become well-known, such as Bravo Zulu (letter code BZ) for "well done", Checkpoint Charlie (Checkpoint C) in Berlin, and Zulu for Greenwich Mean Time or Coordinated Universal Time. In SWAT units, Tango is used for terrorists, Sierra for a Sniper etc.
In addition to the traditional military usage, civilian industry uses the alphabet to combat similar problems in the transmission of messages over telephone systems. For example, it is often used in the retail industry where customer or site details are spoken over the telephone (in order to authorize a credit agreement or confirming stock codes), although adhoc coding is often used in that instance. It has found heavy usage in the information technology industry to accurately and quickly communicate serial/reference codes (which can be and are frequently extremely long) or other specialised information by voice.
Most of the words are recognizable by native English speakers because English must be used upon request for communication between an aircraft and a control tower whenever two nations are involved, regardless of their native languages. English is not required domestically, thus if both parties to a radio conversation are from the same country, then another phonetic alphabet of that nation's choice may be used.
In most versions of the alphabet, the non-English spellings Alfa and Juliett are found. Alfa is spelled with an f as it is in most European languages. The English and French spelling alpha would not be properly pronounced by speakers of other languages—native speakers of those languages may pronounce ph as if it were a p, ignoring the h. Juliett is spelled with a tt for the benefit of native French speakers because they will treat a single t as silent—the English word Juliet is Juliette in French, but the ICAO did not adopt the final e because it might be misunderstood by native Spanish speakers as indicative of a final syllable teh. In English versions of the alphabet, like that from ANSI, one or both may revert to their standard English spelling.

Additions in German, Danish and Norwegian
The letter "Delta" is replaced by "Dixie" at airports that have a majority of Delta Air Lines flights, such as Hartsfield-Jackson Atlanta International Airport.
"Foxtrot" is commonly abbreviated to "Fox" at North American airports.
For Japanese speakers, "Bravo" is difficult to pronounce so in Japan, "Baker" is frequently used instead.
Amateur radio and Citizens' band radio operators will occasionally use "Kilowatt" in lieu of simply "Kilo", and "Radio" instead of Romeo.
In the Philippines, the word "Hawk" is sometimes used for the letter H, rather than "Hotel".
In Indonesia, the word "Lima" for letter L is seldom used since the word "lima" means number five (5) in Indonesian. Instead, "London" is most often used for letter L.
In Brazil, the word "Xingu" replaces X-ray for the letter X. Xingu is a river of the Amazon River system.
Many unofficial phonetic alphabets are in use that are not based on a standard, but are based on words the transmitter can easily remember. Often, such ad-hoc phonetic alphabets are based on (mostly) men's names, such as Alan Bobby Charlie David Edward Frederick George Howard Isaac James Kevin Larry Michael Nicholas Oscar Peter Quincy Robert Stephen Trevor Ulysses Vincent William Xavier Yaakov Zebedee, or on a mixture of names and other easily recognizable (and locally understandable) proper nouns, such as U.S. states, local cities and towns, etc. One documented example of this is the LAPD phonetic alphabet.

Variants
In addition to the alphabets referred to above, numerous other phonetic alphabets have been used in the past.

World War I western front trench slang: Ack Beer Charlie Don Edward Freddie Gee Harry Ink Johnnie King London Emma Nuts Oranges Pip Queen Robert Esses Toc Uncle Vic William X-ray Yorker Zebra This appears to be the origin of the RAF slang phrases such as ack emma for morning, pip emma for afternoon and ack-ack for anti-aircraft. Ack Emma was also used for 'Air Mechanic' in the Royal Flying Corps (1914-18). An oft-quoted origin regarding the term "Ack Ack" is that it comes from the German 'acht-acht' (for "88",) but since the phrase originated in WWI when the Germans employed mainly 75mm anti-aircraft guns (as opposed to the 88 mm guns of WWII,) it would seem to be nothing more than an attractive myth.
British Royal Navy during World War I: Apples Butter Charlie Duff Edward Freddy George Harry Ink Johnnie King London Monkey Nuts Orange Pudding Queenie Robert Sugar Tommy Uncle Vinegar Willie Xerxes Yellow Zebra Older phonetic alphabets
This section has been tagged since May 2007.
In European history, Checkpoint Charlie became an icon of the Cold War. It was a crossing point between East and West Berlin while the city was divided by the Berlin Wall (1961–1989). There were Checkpoints Alpha and Bravo in other parts of Germany, named after the phonetic alphabet for "A", "B", and "C" respectively.
During the Vietnam War, Viet Cong guerrillas and the group itself were referred to as VC, or Victor Charlie; the name "Charlie" has thus become synonymous with this force.
The phonetic alphabet is frequently used in popular culture to evoke a military environment or situation. For example, in the movie Meet the Parents, Robert de Niro plays a former CIA operative who repeatedly utters phrases using the phonetic alphabet.
Other notable examples of usage include the UK television series Juliet Bravo which wasn't the character's name but her callsign, and Robert Ludlum's novel The Bourne Identity which repeatedly uses the system - the phrase Cain is for Charlie and Delta is for Cain is repeated, always italicised, to symbolise the messages relayed to the main character during the Vietnam War.
Slang uses include euphemisms for swear words, such as Whiskey Tango Foxtrot ("What The Fuck?").
Similarly, the Bloodhound Gang's song 'Foxtrot Uniform Charlie Kilo' spells out the word fuck in the phonetic alphabet.

Recordings