never been ona anuclear submarine (museam one that is) but even some diesels from the cold war are classified take HMS ocelot in chatham her oparations are still seacret the boat was first used in the 60's and after all this time stuff is still not allowed to be seen ie log books and such.
HMS alliance a WW2 submarine in gosport is still classified (log books) because she served in the begining of the cold war but she was launched in the 40's
some WW2 oparations are also classified so its not unusualy for some thing only 25 years old to still be classified
did you know that every submarine in russia that includes the old ones and the ones that have sunk are classified and regarded as a state seacret and state property ? any unotharised person going into on on them could result in inprisionment
think yourself lucky that the nautilus is up for show cause theres not many vessels that are
just for the record HMS Victory in portsmouth is still in commission with the royal navy (hence why she can fly the white ensign) and photography isnt realy allowed on her (sign saying so
) but this vessel is over 400 years old still classified?