Remember those drones?

I question the comment about difficulty in shooting them down due to their size and speed. Most, if not all, destroyers are armed with the Phalanx (Goalkeeper) close-in weapon system. It's designed to track and destroy multiple small, fast moving targets at close range. If it can take out naval gun 4.5" or 5" rounds, a drone would be no problem.

That said, unless the drones were clearly hostile, no rules of engagement would allow the firing of hundreds of 20mm depleted uranium rounds with a range of several miles in international waters. The odds of hitting commercial or other shipping or aircraft is too great a risk.