Why did Japanese heavy cruisers receive such large torpedo batteries, and were they useful?
Short answerThey gave smaller ships a way to threaten capital ships in decisive-battle and night-attack doctrine, but their exposed fuel and warheads became a major hazard under attack.
NotesTorpedoes let a cruiser or destroyer threaten capital ships that its navy could not match ship for ship. Furutaka's evolution from six twin tubes to two quadruple launchers shows that reconstruction could reduce tube count while adopting a different offensive fit. Long-range night attacks made the weapon useful in theory and sometimes in practice. Exposed launchers, fuel, and warheads nevertheless created a destructive hazard under air or gun attack, as wartime experience at Midway demonstrated. The Royal Navy increasingly preferred cruiser launchers with overhead protection as the war continued.