Wesley,
You need to get your facts right - it was not the Irish that used the Lusitania for target practise, but the British Royal Navy.
A ploy used by German U-boats during WWII was to lie on the seabed close to a known wreck, preferably one made of metal as opposed to a wooden ship, and lie in wait for an enemy naval vessel or convoy. These wrecks, such as the Lusitania, were well marked on sea charts and when Royal Navy vessels passed over or close by to them, they would pick them up on sonar, recognise them as being wrecks, pass them by, and then they were often fired upon by the U-boat which would surface behind, and ambush them.
The Royal Navy, having lost vessels to this ploy, had a policy of dropping a few depth charges in the vicinity of these wrecks any time one of their vessels came close to them, to destroy or chase away any U-boat which might be lurking beside them. This was done to many other wrecks, the Lusitania being one of them.
There are also those who believe or suggest that the Royal Navy, acting on instructions from the British government or Admiralty, systematically bombed the wreck to destroy evidence that the Lusitania was carrying munitions.
Whatever the reasons, it was the Royal Navy and not the Irish who were responsible for any damage done by explosives.
Regards
Peter