Torpedoes gave small craft a way to threaten much larger ships, but they were poorly suited to fighting enemy small boats and protecting coastal operations. Those jobs called for heavy machine guns and medium-calibre guns on hulls able to carry them. A capable 40 mm weapon would often be enough for fighting other boats, while a 57 mm gun would be especially useful where the hull could support it. Fitting these weapons required space, structural work, and acceptance of the gunboat role. A boat designed around torpedo attack did not necessarily have the capacity for that conversion.
Chapter · 2:55:53-2:59:19
Why motor torpedo boats became motor gun boats
Wartime coastal fighting demanded gun armament and hulls capable of carrying it alongside or in place of torpedoes.