Can the law of countermeasures be used to police the high seas? The freedom of the high seas is guaranteed by the immunity of a State's flag vessels from interference by the public vessels of other States, subject to limited exceptions. However, this rule of non-interference may shield those engaged in unregulated or illegal fishing or transporting weapons of mass destruction and their precursors. This article argues that while such conduct may breach obligations protecting the common interest, unilaterally boarding and arresting a vessel involved would constitute an illegal use of force and cannot be justified as a countermeasure.
* Research student, Trinity Hall, University of Cambridge. I am grateful to the anonymous referee, Professor James Crawford, Dr Andrew Lang, and Ms Kimberley Trapp for their helpful comments.