Did Zuikaku receive concrete-filled underwater bulges after the Battle of the Philippine Sea, and was that a sound idea?
Short answerThe bulges are documented, but the concrete claim needs checking; concrete filling was plausible as a temporary damage-control measure rather than an ideal permanent solution.
NotesZuikaku's bulges appear in the notes consulted during the discussion, but the claim that they were filled with concrete remains unverified. Concrete could be used as a temporary damage-control expedient, yet the interval between the Battle of the Philippine Sea and the carrier's loss at Cape Engano leaves little time for the suggested permanent modification. The notes instead list fire protection, gasoline-tank safety, and removal of combustible fittings, although they may have missed something. A solid fill would add substantial low weight, reduce speed, and transmit shock through the structure, unlike water or crushable piping intended to spread and absorb a torpedo blast. Possible explanations include concrete around magazines, confusion with cemented armor, or cement or clay piping within a bulge. Resolving the claim requires tracing the cited account back through its Japanese source and translation.