Or better yet, CIWS in surface mode.
Which is indeed cool...I saw a live-fire when they were first introduced, and four words:
Wrath of God, Motherfucker. But it'd be a trick getting them aboard merchies.
Like NavAir said, killing the SOB's isn't the problem. We've obviously got the tools at our disposal. It's finding out who's who in the zoo in order to kill the actual pirate scum. The same guys are fishing or running coastal light cargo two days a week, out pirate-ing another two, and zapped out on khat the rest of the time. Shit, they're the only people in Somalia who have jobs. Looking suspicious really isn't enough to light them up, much fun as that would be, and by the time they actually
do anything, it's usually too late and they're aboard the merchie and our problem becomes less War at Sea and more hostage rescue.
Now if we could just get the pirates to start flying Jolly Rogers again, boom, problem solved.
I would bet money that eventually the solution will be a combination of convoy, faster merchies, private security aboard, and a few plausibly-deniable raids when all else fails. Money talks, and the lines are losing money on ridiculous insurance premiums, even if they themselves aren't losing ships.