Pirates

These Pirates off the East Coast of Africa.
They have no political aim, no asylum aim, they are just thieves and murderers.
So, with all the warships in the area (And in the past) why aren’t the small pirate boats being blown out of the water with a 50Cal?

Surely, there are enough troops to put 2 per ship in that area, it would only take a couple of hundred troops to cover all the movements, recycling them back after the ship has docked.