'Principal' (i) was the British overall designation for the contingency plan to be activated in the event that the Vichy French battle-cruiser Dunkerque sortied from the Vichy French North African port of Oran (4/5 April 1941).

Anticipating such a sortie, Vice Admiral Sir James Somerville’s Force 'H' departed Gibraltar on 4 April with the battle-cruiser Renown, the fleet carriers Ark Royal and Furious, the light cruiser Sheffield, and the destroyers Faulknor, Fearless, Foresight and Fortune. The submarines Olympus and Otus had already put to sea from Gibraltar on the previous day to patrol off Oran.

On 5 April the operation was cancelled after it had become clear that the Vichy French battleship was not preparing to leave port, and Olympus and Otus abandoned their patrols off Oran and proceeded to Malta and Gibraltar respectively.