Avast!
I was thinking that a more modern version of the WWI Q-Ship would do wonders in pirate infested waters. Issue Letters of Marque and let them loose!
Q-Ship's initially had success owing to the element of surprise but the Germans quickly caught on.
In WWII, the US built several Q-Ships but disbanded them midway through the war having never sunk a U-boat and with it apparent the U-boats were on guard for them.