In this comparison, six-inch and larger naval shells were excessive for a small, light-framed target. Four-inch anti-aircraft ammunition proved well suited to damaging the same sort of lightly protected, fast-moving construction that made aircraft vulnerable. Its handling and destructive effect were a better match for a fleeting target that had to be disabled before it escaped. This need to kill small craft quickly helped drive the preference for gun-heavy coastal boats.
Notable Point · 23:43-25:32
Why anti-aircraft guns worked against fast boats
The most useful weapon against lightly built fast craft was often an anti-aircraft gun rather than a cruiser or destroyer’s heavier main battery.