Yeah, I own all of them 
The fifth entry was Broadsides and Boarding Parties, a two player game featuring gigantic plastic boats, which was discontinued before the second printing of the series in 1991.
Fortress America is the best of the lot, imo, closely followed and in many ways exceeded by Shogun.
A&A was my first real game, though, so it’s the only one I’ve played more than once (not counting multi-handing).