The Polish border city of Grudziądz (Germ. Graudenz) contained headquarters of the 16th Infantry Division, as well as the military Center of Cavalry Training (Centrum Wyszkolenia Kawalerii). Moreover, it played a crucial role as a strongpoint in order to defend the Vistula River Line and secure the route of retreat of Polish divisions of the Pomorze Army under General Władysław Bortnowski, engaged on the left, western bank of the river. Among units stationed in the Polish Corridor were the 9th, the 15th, and the 27th I.D.'s, together with the Pomeranian Cavalry Brigade from Bydgoszcz. Since Polish headquarters had planned an armed intervention in the Free City of Danzig, the 27th I.D. and the Pomeranian Cavalry had been transferred northwards in mid-August 1939, to the area of Chojnice and