SOME LEGAL BACKGROUND TO "BLIND MAN'S BLUFF"
American Admiralty Books Safety & Privacy Policies (Attention EU Visitors , possible "cookie" encounter ahead)
Some thoughts derived from legal analysis:
1. The intentional uninvited and especially submerged presence of a submarine in someone else's territorial sea is a violation of international law. U.S. submarines during the Cold War, according to "BLIND MAN'S BLUFF entered Russian territorial waters so deeply that according to the book they once were able to read through the periscope submerged cable crossing signs on shore.
2. The operation of a submerged submarine, especially with the intention of intelligence gathering within a coastal state's territorial sea is a violation of international law, yet espionage pretty much remains an internationally tolerated practice and a violation of national law. There seems to be something of a gentleman's agreement for trading intelligence professionals caught in the act, God help the intelligence professional, or submarine crew whose nation doesn't hold any "trade goods".
4. While ill advised there is probably nothing internationally illegal about submerged operations within the exclusive economic zone (EEZ) of a coastal state.