U.S. Navy Guam Silver Handmade Belt Buckle Lettering?

Hello! First let me just say I almost flunked history so please forgive me if I get my facts wrong :). I've seen Navy belt buckles with the word Guam on them and it usually has WWII included in the description. Is that what this belt buckle would be considered? Also does M.I. stand for military intelligence in the Navy? (I'm actually a retired Army spouse, but know nothing about the Navy...or history apparently :). And R.B.Rigg would be the name? I've seen that there was a Robert B. Rigg that was captured by the Chinese and wrote a book but I believe he was an LTC in the army. Were belt buckles like this ever gifted to someone in another branch of service or is that a no-no? Or will I never know who the R.B. Rigg is that had this buckle? I'm pretty certain it's sterling silver (a magnet does not stick and no corrosion on the buckle front). The back is incredibly similiar to one that was sold a couple of years ago that had a reference to Guam and WWII in it, although the front wasn't hand stamped. Thank you so much for any information you have to share.