"affirmative/negative" v. "yes/no"

[Mark Spahn]

In movies, U.S. military personnel say "affirmative" and "negative" 
over two-way radios, instead of a simple "yes" and "no".
(1) Is this an accurate depiction of U.S. military practice?
(2) Is there some reason to use two words that can sound
similar over a staticky radio -- "<garble>ative" -- rather than
two words -- "yes" and "no" -- whose sounds are quite distinct?
If there is a need to have a long word, a simple repetition like
"yes-yes" and "no-no" would be much more distinct from each
other than "affirmative" and "negative" are.
The military goes to the trouble of spelling out words with
letter-names that have distinctive vowel-pairs (e.g., "kilo" for K,
"delta" for D; anybody have the complete list?).
So why do they go out of their way to replace a distinct
"yes/no" pair with an indistinct "affirmative/negative" pair?

-- Mark Spahn  (West Seneca, NY)