The Battle of Jarosław was among the many battles that were fought during the Nazi invasion of Poland. For two days, Polish forces under the command of General Stanislaw Maczek successfully defended Jaroslaw against the Nazi German onslaught. The defensive measures gave enough time for the Polish 10th Motorized Cavalry Brigade to cross the San River and make a safe retreat eastwards. Polish troops were able to repel German attacks, as well as damage and destroy their tanks on the battlefield. Repeated German assaults were equally unsuccessful. Since Maczek had achieved his plan to hold off the Germans, he decided it was time to move his troops further eastward towards the Oleszyce-Lubaczów area. Polish forces blew up the bridges and the majority of troops retreated under cover of darkness, leaving a token force in Jaroslaw. By the morning of September 11 the Germans resumed their assault with heavier artillery, but upon entry into the city, they discovered that the Polish positions had already been withdrawn and were miles away at this point.
Battle of Kepa Oksywska was the bloodiest battle during the German invasion of Poland. It was fought outside the city of Gdynia, in the Oksywie Heights and lasted until September 19, 1939. The Polish army lost about 14% of its forces in the German onslaught. Polish casualties were 2,000 KIA and 7,000 WIA. Polish Col. Dabek had ordered all Polish forces to abandon Gdynia in order to save the civilians from complete annihilation. The battle ensued in the Heights. Until September 14 Polish forces gradually withdrew to the area, converging within a space of no larger than 4 square kilometers. At this juncture the Poles, who were numerically and technically overpowered by the Germans, were still able to inflict heavy casualties on German forces. Within the next five days, there were no fewer than 110 skirmishes fought in the enclosed space of 4 square kilometers. Despite successful counterattacks, the Polish troops were ordered by Col Dabek to cease-fire on September 19. The heavy German bombardment and dwindling Polish supplies left no other alternative. Col. Dąbek committed suicide, rather than surrender.
Battle of Łomża took place in Lomza on both sides of the river Narew. During the German invasion of Poland, the river line was occupied by the Polish Independent Operational Group Narew, which consisted of two infantry divisions and two cavalry brigades. The objective of the infantry was to defend the Narew line of vital bridgeheads at Różan, Ostrołęka, Osowiec Fortress, Nowogród, Łomża and Wizna, and to shield the right flank of the Modlin Army, while the Polish cavalry had to organise delaying actions along the Polish-German border and at the Biebrza River (to the north-east of Łomża). On September 3, the Luftwaffe launched several massive aerial bombing runs against Lomza, but the Poles suffered only negligible losses. German troops which broke through the the Polish Corridor into East Prussia reached the outskirts of Lomza by September 7, but their attacks were repelled by fierce Polish machine gun fire and 37mm Bofors anti-tank guns. In the ensuing battle the Germans suffered heavy casualties including the loss of 6 tanks. The next day the Germans attacked forts II and III, but were still repelled by heavy Polish fire power. By mid afternoon the German commander ordered air support from the Luftwaffe, which heavily bombed fort III and the bridge across the Narew, causing heavy Polish losses. Despite these assaults, and renewed German attacks, the Polish positions were unshakeable. On September 10, yet again the Germans repeated their attacks against the formidable forts no. II and III and even with the added support of German bombers could not destroy a single Polish bunker. Consequently, the Germans had to get out of range of Polish artillery fire. With Polish morale very high at this point, Col. Stefan Kossecki, commander of the 18th Infantry Division, ordered the Polish troops to abandon Lomza. The reason was that Germans had won the Battle of Nowogrod and the Poles failed to retake the town. German troops later captured Lomza without the use of force and on September 29, they handed the town to their Soviet allies.