A destroyer optimized for air defense still needed to damage surface opponents quickly. Torpedoes offered a powerful attack, but a missed salvo left the enemy able to continue fighting. Gunfire could progressively damage a target and inflict a mission kill by preventing it from fighting back. Japan's 100 mm weapon therefore involved a tradeoff: its anti-aircraft qualities did not provide the shell effect wanted against enemy destroyers or larger ships.
Notable Point · 6:21-7:48
Why torpedoes did not remove the need for destroyer gunfire
Gunfire could disable an opponent even without sinking it, giving destroyers a surface-combat requirement that torpedoes alone could not satisfy.