They won't capitalize "scuba", since it's now just a regular word. But for proper nouns, they distinguish "acronyms" (like Nasa) from "intialisms" (like FBI).

They won't capitalize "scuba", since it's now just a regular word. But for proper nouns, they distinguish "acronyms" (like Nasa) from "intialisms" (like FBI). An acronym is pronounced like a word, so they treat that word as a proper noun (capital first letter, others lower case). That can be informative about pronunciation. The BBC writes the World Health Organization as WHO, not Who.