The first cut ain't the deepest, and X doesn't mark the spot of it. The former HMAS Adelaide is being cut open (well, partly open) in anticipation of being scuttled as a dive wreck.

The orange flame of a torch can be seen cutting holes in the side of her hull, making me think that the preparation for her sinking is reaching its final stages.

I'm no old sea dog (which is an understatement bordering on sarcasm) but I believe that the purpose of doing this is to make sure that Adelaide floods evenly when she goes down. That means no air pockets, which in turn means no unfortunate jagged edges from the sides of the hull going "KABLOOEY!!!" during the descent. (Find some images of the state of Titanic's stern section (which, unlike the bow, wasn't flooded before she sank and therefore had a lot of air captured inside) to get some idea of the difference.)

It's crazy enough to be diving on old ships as it is, much worse when you can get grated to pieces doing it.
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Edit September 2023: I may have THOUGHT that the end was nigh... but as it turned out thanks to NIMBY campaigns it was still more than a year away.