There are navies that has been doing this for many years. On a side note: generally speaking an SSK is much quieter than any nuclear propelled submarine, mainly due to that an SSN's and other nuclear subs' cooling system has to be running all the time, to cool the reactor. There are of course...
I know this is a very late reply to a thread that is probably forgotten, but I could not resist commenting.
I have been working with Submarine design for over 16 years with submarines of three countries and have quite an insight to german designs as well. The Gotland even though it is older...