The NATO phonetic alphabet, more formally the international raiotelephony 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 (Alfa for A, Bravo for B, etc.) 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.