They were sinking that ship in a specific spot to create a reef and playground for divers. They removed all the equipment to prevent polution. Do I need to point out that those considerations take a backseat in wartime? Many US carriers were taken out by a single bomb, because they were built with wooden deck, unlike British carriers which had armoured decking.
Frigates and destroyers have been a platform for torpedoes for many years, it's pretty obvious their pop guns are not going have any affect on a battleship, but they are not facing battleships are they.