The same month, the States General, becoming ever more concerned by the expansionary plans of the Swedish king, Charles X, decided to intervene in the Second Northern War by sending a fleet to the Baltic Sea. The Swedes controlled this area after Charles had invaded Poland and claimed the Polish throne. De Ruyter once again embarked aboard the "Tijdverdrijf", arriving at the Øresund, where he waited for Obdam to arrive on 8 June. After Obdam had assumed command, De Ruyter and the Dutch fleet sailed to relieve the besieged city of Danzig on 27 July, which they did without any bloodshed. Peace was signed a month later Before leaving the Baltic, De Ruyter and other flag officers were granted an audience by Frederick III of Denmark. De Ruyter took a liking to the Danish king, who later became a friend.