Japanese suicide boats could thread along the coast through water too shallow for destroyers to follow. That geography created an approach route toward the invasion beaches that large escorts could not close. Armed small craft and converted gun landing craft could operate in the same confined water and often destroyed the attackers before they reached the landing zones. Draft and access could therefore matter as much as speed or firepower in littoral defence.
Notable Point · 58:49-59:17
Shallow water gave armed small craft a defensive niche
Japanese suicide boats could move along shoreline routes too shallow for destroyers, making armed shallow-draft craft essential to the beach perimeter.