NGS Style Manual‎ > ‎- M -‎ > ‎

MILITARY UNITS

Spell out and capitalize military units through Tenth:
            Second Battalion
            First Cavalry
            Sixth Fleet
            First Marine Division
            474th Fighter Wing

Use Roman numerals for corps:
            XVI Corps.

Capitalize but do not quote nicknames of units:
            Green Berets
            Rainbow Division

See also:      AIR FORCEARMY, MARINE CORPS, NAVY
                        armed forces, armed services, special forces
                        MILITARY RANKS
                        Ranger, Rangers, SEAL, SEALs
                       TITLES OF PERSONS.