Merchant marine -- National security -- 3 Prevention 3 Security measures 3 Terrorism -- 3 History -- 2 Security measures -- 2 more ... Shipping -- 2 Boats and boating -- 1 Certification -- 1 Civil defense 1 Civil defense -- 1 Congresses 1 Congresses -- 1 Defenses 1 Globalization 1 Harbors -- 1 Hijacking of ships -- 1 History 1 International relations 1 Maritime terrorism -- 1 Merchant mariners -- 1 National security 1 Naval art and science -- 1 Navigation -- 1 Officers -- 1 Pirates 1 Politics and government -- 1 Prevention -- 1 Safety measures 1 less ...