There is a story that the third torpedo ended up embeded in the hull of one of the escorsts.This has subsequently been dissmissed as a good dit. Belgrano was the HVT, that is why she was sunk. Shars are not much good with out a deck to fly from and her battle group was a threat to our carriers. Her demise caused the Argentine Navy to run for home. So quickly, according to legend. that the boat that was watching "25 May" could not engage as the carrier turned tail 30 mins before the boat could shoot.
The MK8 was selected because Concs had never been able to succesfully fire a Tigerfish.
If you want to know more read "Sink the Belgrano" by Mike Rossiter