On the sinking of the "Ark Royal" - I remember it used to be used as a model exercise at HMS Pheonix (Royal Navy NBCD school). From dim memory the instructor put one of the major causes of her ultimate loss down to the poor control of the fire-fighting parties who managed to put the ship into a state of loll, his (the instructor) comment was that 4 inches of free surface water sank the Ark, much the same happened to the Normandie in New York harbour.

One programme I watched on the Titanic mentioned the steel and the rivets - I suppose that quality control and NDE inspection techniques were not up to the mark at the time she was built.

The Liberty ship problem, I thought was one of inadequate stress relief at the hatch corners which caused the cracks to appear and propogate.