I've also heard the story about the Argentine Navy's somewhat casual attitude about condition zebra.
And you're right about what Belgrano would have been able to do to any British force on the island.
Look out/Look out/Look out for Jimmy Valentine ...
The Belgrano was sunk by a salvo of three Mk 8 torpedoes from HMS Conqueror. Either one or two of these hit. The Mk 8 was an unguided, steam powered torpedo developed in the 1920s.
Why was a modern nuclear submarine using unguided torpedoes designed 60 years ago? Because the "modern" Mk 24 electrically powered homing torpedoes didn't work.