Could a 57 mm gun fire a useful anti-UUV round, and what is the smallest practical calibre for such a weapon?
Short answerA 57 mm weapon might work against small or shallow targets, but larger smart shells or a modern Hedgehog-like system offer more reliable underwater explosive effect.
NotesA 57 mm shell may work against shallow or lightly built targets, but useful underwater blast effects generally push designers toward larger 4.5- or 5-inch rounds. The discussion distinguishes UUV defence from attacking full-size submarines and favors area effects when a precise underwater firing solution is unavailable. Reusing a ship's main gun reduces deck-space, ammunition, maintenance, and training burdens compared with adding a wholly separate launcher. A programmable common round able to support anti-air, surface, land-attack, and limited underwater roles would therefore have considerable logistical value.