Brevity codes are used by the military (mostly Air Force personnel), to convey convex information in a few words. Here’s a list of American/NATO Multiservice Tactical Brevity Codes. As far as I know, the codes for alphabets that the Indian defence services use are (corrections/additional info welcome):
If you notice carefully, these codes are designed in a way that when somebody is saying them over a noisy radio connection, no two alphabets can be confused with each other. Each of them has a unique sound and has as few syllables as possible (and no silent letters).
Further, all over the world, to reduce confusion between one and nine, the latter is commonly substituted by niner.
Zulu also refers to GMT time.