Delta — NATO Phonetic Alphabet for D

D's word, Delta — said "DELL-tah" — never itself needed replacing. It's one of the words that survived from the alphabet's original 1951 draft straight through to the final 1956 standard unchanged.

A Word That Nearly Caused a Different Change

Delta itself was never the problem during testing, but its similarity to "Extra" — the original 1951 word for X — was cited as a real source of confusion under noisy radio conditions, and it's part of why Extra was eventually replaced with X-ray in the 1956 revision rather than Delta being the one to change. In everyday aviation use, some U.S. airports have also substituted alternate words like "David" for D specifically to avoid controllers confusing an ordinary use of the letter with Delta Air Lines' own airline callsign. The word also carries a second, entirely separate international recognition path: delta (Δ) is the fourth letter of the Greek alphabet and widely used in mathematics and science as shorthand for "change," a meaning many people already know before they ever learn it as a phonetic-alphabet word.