The NATO phonetic alphabet, officially denoted as the International Radiotelephony Spelling Alphabet, and also commonly known as the ICAO phonetic alphabet, and in a variation also known officially as the ITU phonetic alphabet and figure code, is the most widely used radiotelephone spelling alphabet. Strict adherence to the prescribed spelling words is required in order to alphabet 26 numbers the problems of confusion that the spelling alphabet is designed to overcome. It is known that has been prepared only after the most exhaustive tests on a scientific basis by several nations.
One of the firmest conclusions reached was that it was not practical to make an isolated change to clear confusion between one pair of letters. To change one word involves reconsideration of the whole alphabet to ensure that the change proposed to clear one confusion does not itself introduce others. The same memo notes a potential confusion between ZERO and SIERRA is overcome when following the procedures in ACP 125, which specify the use of the procedure word FIGURES in many instances in which digits need to be read. The same alphabetic code words are used by all agencies, but each agency chooses one of two different sets of numeric code words. This section needs additional citations for verification. For instance the message “proceed to map grid DH98” could be transmitted as “proceed to map grid Delta-Hotel-Niner-Ait”.
Using “Delta” instead of “D” avoids confusion between “DH98” and “BH98” or “TH98”. In addition to the traditional military usage, civilian industry uses the alphabet to avoid similar problems in the transmission of messages by telephone systems. This article contains IPA phonetic symbols. The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities.
The qualifying feature was the likelihood of a code word being understood in the context of others. For example, football has a higher chance of being understood than foxtrot in isolation, but foxtrot is superior in extended communication. The pronunciation of the code words varies according to the language habits of the speaker. To eliminate wide variations in pronunciation, recordings and posters illustrating the pronunciation desired by the ICAO are available.
Pronunciations are somewhat uncertain because the agencies, while ostensibly using the same pronunciations, give different transcriptions, which are often inconsistent from letter to letter. Only the ICAO prescribes pronunciation with the IPA, and then only for letters. The IPA form of Golf implies it is pronounced gulf, which is neither General American English nor British Received Pronunciation. ICAO has different stresses for Bravo, Juliett, X-ray in its respelled and IPA transcriptions. Also, the ITU and IMO specify a different pronunciation of numerals than does the ICAO, using compound words combining the English word with either a Spanish or Latin prefix. However, as of 2002, the IMO’s GMDSS procedures permit the use of the ICAO numeral pronunciation. Prior to World War I and the development and widespread adoption of two-way radio that supported voice, telephone spelling alphabets were developed to improve communication on low-quality and long-distance telephone circuits.