While I disagree with the main gist of the article (I feel the vessels have a right to be armed for protection), it is well thought out and worth reading.
http://piratebook.blogspot.com/2009/11/escalation-of-weaponry-off-horn-of.html
Here is the article mentioned in the piece - http://gcaptain.com/maritime/blog/anti-pirate-weapons-piracy-somalia/ and another here - http://gcaptain.com/maritime/blog/10-more-anti-piracy-weapons-for-use-in-somalia/