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.
I didn't know that about the Brit torpedoes. Thanks.