Given the state of Japanese shipbuilding at the time (i.e. scrambling for whatever they could lay their hands on) and the questionable quality of their damage control techniques even at the height of the war, I'd say it was the classic "little of column A, little of column B." Namely bad design compounded by incompetent damage control that both drew from the same well of late-war woes.

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CdrMike, Overwatch Reject