Easy target.

Just saw Captain Phillips. While it was a good movie and Tom Hanks was terrific, I wish they had explained why a ship that large traveling in perilous seas did not carry any arms. It seems to me the entire situation could have been avoided if the ship's crew of twenty could have fired upon the two skiffs that were approaching the ship, and certainly the one with only four pirates who actually came aboard. Since it was a true story, I can only assume there were no guns aboard. But why?