Lithuania supported it and the knights threatened to invade. Poland announced its support for the Lithuanian cause and threatened to invade Prussia in return. As Prussian troops evacuated Samogitia, Teutonic Grand Master Ulrich von Jungingen declared war on the Kingdom of Poland and the Grand Duchy of Lithuania on 6 August 1409.[22] The Knights hoped to defeat Poland and Lithuania separately, and began by invading Greater Poland and Kuyavia, catching the Poles by surprise.[23] The Knights burned the castle at Dobrin (Dobrzyń nad Wisłą), captured Bobrowniki after a 14-day siege, conquered Bydgoszcz (Bromberg) and sacked several towns.[24] The Poles organized counterattacks and recaptured Bydgoszcz.[25] The Samogitians attacked Memel (Klaipėda).[23] However, neither side was ready for a full-scale war.