In 1658, the States General, on the advice of a leading member, Cornelis de Graeff, one of the mayors of Amsterdam, decided to once again send a fleet to the Baltic Sea to protect the important Baltic trade and to aid the Danes against Swedish aggression, which had continued despite a peace settlement. In accordance with the States' balance-of-power political approach, a fleet under Lieutenant-Admiral Jacob van Wassenaer Obdam was sent without De Ruyter, who at the time was blockading Lisbon. On 8 November, a bloody melee took place, the battle of the Sound, which resulted in a Dutch victory, relieving Copenhagen. Still the Swedes were far from defeated and the States decided to continue their support for the Danes. De Ruyter took command of a new expeditionary fleet and managed to liberate Nyborg in 1659. For this, he was knighted by King Frederick III of Denmark. From 1661 until 1663, De Ruyter did convoy duty in the Mediterranean.