i dont know if you consider the falklands as argentinian mainland, wich I do, but still, a british submarine sunk the Belgrano out of the engagement area breaking international treaties.
Also, one british ship was damaged from one of the coastal cannons and another, (the sheffield i think) was sunk after an air assault.

now, for the following i dont have confirmation but ive heard that the uk had nuclear missiles targeting buenos aires in case somethig went wrong, fortunately, since the british won, there was no need for that.

again, i colud be wrong so if anyone has some relyable information feel free to correct me

gabriel