Punching underwater

Is there any benefit to punching or shadowboxing under water? I read this was one of Rocky Marciano's favourite exercises and he's famous for his devastating power. Has anyone else benefited from this exercise or made it part of their regular workouts?

I use to do it every day back when I lived in Florida,
in all honestly, with all respects to the Rock it did
not do much for me. He used to uppercut and
hook under way as fast as he could. Give it a try,
you never feel fatigued after it.

He would tread water and do this for an hour at a time when he stayed at hotels, I believe. This was AFTER he would duck-walk up twenty or so flights of stairs. Ever try duckwalking, just on a flat surface? Now imagine doing that UP stairs, up to the top floor of a tall building! Perhaps it was the strength and endurance of his legs that helped him stand upright and even walk through some of the brutal beatings he received.

its dragging your feet while squatting down and walking accross the room. famous wrestling endurance workout

The rock did a WHOLE BUNCH of things other than punch in water and duck walk. I read in an article that he punched a bag that was SUBSTANTIALLY over 150lbs. (I'm tempted to say 300lbs., but I frankly don't remember). Apparently, he just broke the 150lbs. bags with ease, so he switched.