After the outbreak of the Polish Defensive War the division entered in contact with the enemy on the first hours of the conflict. Attacked by the German XXI Corps of the 3rd Army, the division was pushed back to the other side of the Osa river. Suffering from a nervous breakdown, the commanding officer ordered his forces to retreat, but was soon replaced with Col. Zygmunt Szyszko-Bohusz, until then the deputy commander of the division. The latter prepared the plan of a counter-attack on the flank of the advancing Germans, but the fast pace of their advance cut out the Pomorze Army in two and the attack was called off.