The Historic Dockyard in Chatham is also worth seeing - interesting museum ships plus several museums (and nearby is the Royal Engineers Museum).
The Fleet Air Arm Museum in Yeovilton is from the photos I have seen also well worth a visit, it both has a lot of naval planes and some good ship models.
The Royal Air Force Museum Cosford is very impressive.
In London HMS Belfast is for sure interesting, I was a little bit disappointed by both the Imperial War Museum and the National Maritime Museum. Both lack good ship models, especially the later contain only good ones from the sailing period. Very good ships models were in the Science Museum, but this department of the museum was closed to my knowledge.
In Cherbourg is the La Cité de la Mer containing Le Redoutable, a SSBN as museum ship.