In 1609, the Dutch jurist Hugo Grotius noted that ‘because the sea is fluid and ever changing, it cannot be possessed.’ 1 This statement has lost nothing of its plausibility. How then could anyone ever argue that a state could aspire to ‘command of the sea’ or to ‘rule the oceans’? This chapter seeks to explore the origins of a concept which was always an overstatement of ambitions, to the point that it is difficult to understand how it ever came into being.