Mmmm.....Ok, there are two Marina's in Portsmouth, one is at Gunwharf Quay's but has only been there for about five years (max). And is quite small.
The main Marina is called "Port Solent" and is large, but I can't think of any submarine display there, and I go there quite often. Just over the water, either by Ferry, or by driving round the motorway, you have Gosport, where the Royal Navy Submarine Museum is....they have a Submarine on display that you can walk around (Guided Tour), but this is a full size submarine from the sixties/seventies.
Inside the museum its-self, there are some one man submarines....one of which was the submarine which was rebuilt on one of the TV Programmes....it was actually a german one man submarine, but there are quite a few other ones there now.....But not the one used in any of the Bond Films.
Can you remember if the marina you were in was full of yachts, or old naval patrol boats.......If it was all ex navy ships, then you were in the Naval Dockyard, which is a really entertaining day out now, if you visit the old warships.....HMS WARRIOR & VICTORY. If it was in a marina with yachts in, then you were at Port Solent....where there are alot of bars/restaurants right on the edge of the marina, and overlooking all the yachts.
If you do come down, drop me a PM and we'll have a meet for a beer.
Southsea is great during the day, but now all the best Night Clubs are at the Guildhall Square (About ten all next to each other) or at Gunwharf Quays where you have Tiger Tiger....

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All the best
Jim