Hi Meanee, welcome to CruiseReviews. There really isn't much deep diving in either St. Maarten or St. Thomas. The TikiHut had a cannon that was sunken and some of the fort, I think I remember a submarine there, too (St. Maarten). St. Thomas has some good snorkeling/diving but mainly sport diving, around 30'. Buck Island might be a good place for you to go. However, I still recommend Trunk Bay. Even though it's snorkeling, the water is crystal clear (unless there's a storm). There are no wrecks, just coral and fish, but the beach is magnificent.
For good diving, Grenada's Flamingo Bay, Bonaire-just about anywhere, Dominica's Champagne Reef, and Belize/Roatan Reefs.