One of my coworkers and i had a civilized argument about Master Chief's rank. He swears that MC is a Marine, I told him," Nay, Master Chief is a Navy Special Forces Operative, as is every other Spartan."

I've been thinking, and i do that alot, about Master Chief's training.
I've heard people say he's a Marine, and others say he's Army. Well, he's neither. Master Chief is Naval Special Forces (i.e. SEALs)
Here are my reasons for this:
1. Master Chief Petty Officer isn't a Marine rank, it's Navy and Coast Guard.
2. The Spartans act like Infantry with special equipment, which makes them Naval Special Forces.
3. Dr. Halsey, in The Fall of Reach, stated "You have been called upon to defend Earth...You will become the best the Navy has." (Hasley to the Spartan Trainees)
So i believe my argument is valid.
Master Chief