1) Giant Octopus that attack your sub in the North/East Pacific. (Just saw this on the Discovery Channel)
2) Option to jettision dead crew members and garbage from the Torpedo Tubes. As well as, ejecting Oil Sludge from tanks. This is to fool the enemy of course. :hmm:
3) Unlock a secret easter egg, which is another sub. Specifically, Captain Nemo's sub the Nautilus. Man, that would be cool, and open up all kinds of crazy new missions.
I know... This is crazy.
