There's about a 90% chance you're going to contact me in less than a month so I may as well address this now. The total extent of marine corps involvement in EAME is given at Message #6130. Period. Send a signed request, with your your uncle's full name to:
Bureau of Naval Personnel Liaison Office, Room 5409 9700 Page Avenue St. Louis, Missouri 63132-5100
They won't tell you everthing without his written consent but they will provide limited information.
The naval personnel Turner refers to were (and are) Beachmasters. Their primary duties were (are) to co-ordinate the landing of men and materiel and direct their movement off the beachhead and inland. Period. Their exposure to actual combat was minimal- to non-existent but that wasn't part of their official duties, anyway.
What Turner "...doesn't know..." or "...has never quite understood..." would fill a multi-volume set - if not a library - and although expressions like, "overlay of authority", etc. sound impressive to the initiated, they're totally meaningless.