This article revises previous interpretations of the Imperial Maritime League, and adds new detail to our understanding of Edwardian patriotic leagues, by highlighting the relevance of radical right ideology. A product of division in the Navy League, the Imperial Maritime League channelled extra-parliamentary sentiment into specific navalist causes, and worked closely with likeminded newspaper editors and naval officers to challenge the Unionist leadership, Admiralty, and Navy League. The new league was ultimately undermined by British victory in the naval race, and the Navy League's preparedness to react positively to the challenge of a new navalist league.