Japanese planners did not believe Americans were incapable of submarine warfare. The Imperial Japanese Navy recognized the potential threat but overestimated what its existing escorts and doctrine could do about it. Japanese anti-submarine forces had developed useful experience around the First World War and then allowed parts of that capability to atrophy. Confidence in an outdated institutional memory concealed the need for more ships, training, and convoy organization. The failure came from misjudging Japanese preparedness rather than simply dismissing the opponent.
Notable Point · 2:27:09-2:27:30
Japan understood US submarines but overestimated its defenses
Japanese planners did not dismiss American submarine skill, but they trusted anti-submarine capabilities derived from First World War experience that had since atrophied.