 Wallenstein, who had nevertheless managed to build thirteen vessels in Wismar under Philipp von Mansfeld, was unable to use them, because Swedish ships were blockading that port.Christian IV concluded an alliance with Gustavus Adolphus of Sweden in April, and both supported Stralsund in her successful resistance against Wallenstein.In August, an attempt to secure another bridgehead on the southern Baltic shore failed with Christian IV's defeat in the Battle of Wolgast.