Flag State Responsibility: Who Answers for a Ship at Sea

Flag state responsibility means every merchant ship answers to one country. That country is the state whose flag it flies. It writes the registry rules and surveys the hull. It checks the crew's papers and investigates casualties. International law assigns the duty. Port inspections exist because the duty is not always met. The duty is written in treaty text. Article 94 of the United Nations Convention on the Law of the Sea sets the rule. The 1982 treaty is often called UNCLOS. It requires every state to "effectively exercise its jurisdiction and control" over ships flying its flag. The control covers administrative, technical, and social matters. The stakes are wide: as of 2025, more than half of the world's merchant tonnage sails under open registries. The guide to the Posse Comitatus Act and naval power marks another boundary of state authority; the policy section gathers more guides to law at sea. What Does the Law Require of a Flag State? The convention text is specific.

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