In the midst of this, in 1637, De Ruyter became captain of a private ship meant to hunt for the Dunkirkers, raiders operating from Dunkirk who were preying on Dutch merchant shipping. He fulfilled this task until 1640. After this, he sailed for a while as skipper of a merchant vessel named "De Vlissinge". In 1641, De Ruyter was nominated by the Admiralty of Zeeland to become the captain of the "Haze", a merchant ship converted man-of-war carrying 26 guns, in a fleet under admiral Gijsels formed to assist the Portuguese in the Portuguese Restoration War against Philip IV of Spain, who was also Philip III of Portugal. The Dutch fleet was to join a Portuguese squadron fighting Spain at sea, and De Ruyter was appointed to be its "Schout-bij-nacht" or third in command. Although this expedition had little success, De Ruyter distinguished himself in combat against a Spanish fleet in the inconclusive action on 4 November 1641, off Cape St. Vincent. However, as a result of the loss of two ships and damage to others in this action, and the withdrawal of the Portuguese squadron after the action, the Dutch fleet returned home without completing its mission.