It is in fact close to impossible to sneak a sub into the black sea, although it can be done. The waterway into the black sea (The Bosporus) is an extremely narrow channel and kind of shallow for a sub to get through. Any ship has to get permission way in advance to get through. And going underwater at periscope depth I think is the deepest you can go, you must stay behind a rather large ship in order to keep your wake trail out of vision. Not only this, but you gotta have the latest charts and information available to avoid wrecks, rocks, etc to get through successfully, not to mention a pro commander :).

All of this was outlined in a great book about Naval Warfare and politics I read, its called Nimitz Class. (Its about a Russian Kilo that sneaked through the Bosporus and sunk most of a US carrier battle group with a nuclear torpedo.) Very cool book I thought.

Aah, Nimitz-class, the only book that Robinson ever wrote that doesn't manage to make you root for the bad guys...

Ha, the only one I read. Any others of his good?

Well...the only I've read was Ghost Force. Honestly, I wasn't very impressed; regardless of plot reasons, Type 45s should not lose to Skyhawk fighters. I felt that his writing style just wasn't up to the standard set by Tom Clancy or Fred Forsyth.

But that's just my opinion; I understand that Robinson's a popular author around these parts.

About russian forces
 

Just because you are talking about russina forces and about a DW mission in the black sea....and molon labe had a look to google earth.... I just have a look to the Polyarnyy, "the red october base", and I could distinguish some surface ships and 5 subs docked there, but I can't tell the type of none. Maybe you also want to have a look to it.