In the northwest, the German Army Group North under Fedor von Bock attacked Pomerania and Greater Poland, moving from Germany proper (German Fourth Army) and from East Prussia (German Third Army). In the Battle of Tuchola Forest that lasted from 1 to 5 September, they split the Polish Army Pomorze under Władysław Bortnowski which was tasked with the defence of the Polish Corridor; parts of it under Admiral Józef Unrug would continue to defend pockets of the coast over the next few days or weeks (at the Battles of Westerplatte, Gdynia, Hel and others) while the rest was forced, together the Army Poznań under Tadeusz Kutrzeba, to retreat east from their defensive lines in Greater Poland towards Kłodawa in Kujawy.