This is also true for initialisms, which are acronyms in which each letter is pronounced individually.
“A NASA project” would not become “an NASA project” because nobody pronounces each individual letter of NASA, they just say it as one word.
“An FBI agent” would always be correct, and “a FBI agent” would always be incorrect, because FBI is never pronounced as a word, and each letter is pronounced individually.
This is also true for initialisms, which are acronyms in which each letter is pronounced individually.
“A NASA project” would not become “an NASA project” because nobody pronounces each individual letter of NASA, they just say it as one word.
“An FBI agent” would always be correct, and “a FBI agent” would always be incorrect, because FBI is never pronounced as a word, and each letter is pronounced individually.