"The Coast Guard has received a number of questions from U.S. vessel operators and company security officers over concerns about compliance with U.S. law when placing firearms on board their vessels to defend against or deter pirate attacks in high-risk waters. The Coast Guard has worked closely with the Department of Justice, and the Department of State's Directorate of Defense Trade Controls (the agencies responsible for the International Traffic in Arms Regulations [ITAR]), and Customs and Border Protection (CBP) (the agency responsible for enforcement of ITAR), to provide guidance for owners, operators, and security teams of U.S. --flagged vessels who want to place firearms aboard vessels. It outlines potential methods of compliance but does not replace the underlying regulations. This guidance does not address foreign-flagged vessels."
Port Security Advisory (4-09)(Rev 3)
United States Coast Guard: http://homeport.uscg.mil/