Submarines are very capable at Signals Intelligence (SIGINT), traditional Human Intelligence (HUMINT) operations as well as Special Operations.
The following is a fragment of a slightly longer article “War Patrol The Falklands - HMS Onyx” (retrieved July 25, 2018) based on original Source: The Submariner 03/2004 in RN Subs: Website of the Barrow Submariners Association. New links added in [...].
“...[the conventional sub - SSK HMS] Onyx had a double role, as well as adding the submarine deterrent, she could also be employed in reconnaissance and "cloak and dagger" operations, taking periscope photographs of enemy installations and likely landing areas for small groups of Special Forces. Onyx was better suited for this as she could move closer inshore where her silence of operation afforded her extra protection.
At Ascension Island, she picked up yet another cargo of SAS/[SBS] men trained in the clandestine arts of sabotage ashore for a series of operations. The crew worried about them every time they left, as it wasn't always the Onyx who picked them up again. [From Wiki "Contrary to some reports, after the British cancelled Operation Mikado, there was never a plan to use Onyx to land the SAS in order to destroy Argentina's remaining stockpile of Exocet missiles. Prior to the submarine being damaged the SBS had been embarked to attack a mainland airfield but this operation, too, was cancelled.]
One of the biggest problems was the navigational information available. [Even in 1982] The charts for this part of the globe were mainly signed by one Captain James Cook over 200 years ago [including South Georgia island, in 1775, which is near the Falklands. South Georgia was also occupied by Argentine forces during the Falklands War]. The give away was where the distance between the soundings of the seabed got to be five or ten miles apart. Onyx hit one rock that James Cook missed which put a bit of a dent in the front end of the submarine..."