Maritime Security Directive 104-6 (Rev 6); Guidelines for U.S. Vessels Operating in High Risk Waters, Notice of Availability [open pdf - 152KB]
"The Coast Guard announces the release of Maritime Security (MARSEC) Directive 104--6 (Rev 6). This Directive only applies to U.S.-flagged vessels subject to the Maritime Transportation Security Act (MTSA) on international voyages through or in designated high risk waters, and provides additional counter-piracy guidance and mandatory measures for these vessels operating in these areas where acts of piracy and armed robbery against ships are prevalent. MARSEC Directive 104--6 (Rev 6) also includes an annex that provides specific direction for vessels operating around the Horn of Africa. Although MARSEC Directives are designated Sensitive Security Information (SSI) and are not subject to public release, a non-SSI version of this directive is available."
Federal Register: http://www.federalregister.gov/
Federal Register (January 30, 2012), v.77 no.19 p.4573-4574