Swarms of small and cheap vs. ... what? That bow machine gun is probably .30 or .50 caliber. It might be effective against personnel in a boarding attempt. Against an armed naval ship with remote-controlled-by-radar guns and cannon, no. And AC-130s and A-10s have pretty decent loiter times. And MQ-9s have 14 hours' endurance, fully loaded, so probably 10-12 hours' loiter time in the critical area, depending on where they are based. Once Iran started with more than harassment, taking out their boats would soon be followed up by their bases and building yards going "Boom!"