The important thing about tracking military careers is not so much where they were 'from' but what organization they were in.
In the case of the Revolutionary War: Militia? State Troops?Continental Army?What Regiment/Battalion?Then one canWhat unit was he in?Are you talking about the MD Captain by thfigure out what activity they might have been involved in and where records might be.
According to Heitman's /Historical Register of Officers of the Continental Army . . . ./ a Capt. James Williams started out in the 10th VA Reg't. (Continental) which was consolidated and renamed the 6th VA Reg't. in May 1779.The entire regiment was captured at Charleston.
I did not find a listing for a VA Capt. (or other VA officer) named Charles Bruce.
I am sure there must be some specific lists of Charleston captives in the British military records, Colonial Office manuscripts, British Archives, Kew, England -- but to the best of my knowledge they have not been published.