In May, the objective of the Designated Formation was described in more detail – it was to create a defensive line in the area of Branica, Brzeźce and Wisła Wielka, shielding the division's main positions. Cadet officers and soldiers prepared a line of forward defense posts, which – after the cadets had completed their training and took their final exams in July – were filled with soldiers of the 20th Infantry Regiment’s 3rd Battalion (commanded by Maj. Tytus Brzosko) and the 4th Battalion of the 16th Infantry Regiment (under Maj. Stefan Rachwał).
In the morning of 1 September 1939, a German tank battalion of the 5th Armoured Division of General von Vittinghoff reached this position. Three charges in a row broke in the anti-tank guns fire. The enemy, having lost 29 combat vehicles, retreated to their starting position.
During the night of 1st September, the Regiment’s main forces marched from the Zator area, where the 6th Infantry Division was concentrated, to Pszczyna and Ćwiklice. The 1st Battalion, which was the Regiment’s reserve, was deployed to the palace park in Pszczyna, the 2nd Battalion defended a seven-kilometre section from Goczałkowice on the bank of the Vistula River to Pszczyna, while the 3rd Battalion manned a four-kilometre stretch from Pszczyna to Stara Wieś. The defensive position consisted of a single trench protected by barbed wire fences, 16 concrete bunkers equipped with heavy machine gun and several wooden battle shelters with light machine gun positions. Behind them, in the Ćwiklice area, without any field cover, 12 cannons of the 6th Light Artillery Regiment’s 2nd Battery under Maj. Jan Gintel, as well as the Regiment's command post, were stationed.
Around 10 o'clock, the main forces of the 5th Panzer Division – tanks supported by motorized infantry – fell on this line of defense. After about half an hour, the positions of the 3rd Battalion were breached, and the German tanks managed to break through the defense line. Neither infantry, stretched thin over a wide section, nor the unprotected and uncovered cannons could stop them. By 12 o'clock, the Polish defense in the area of Stara Wieś had ceased to exist. An order was given to evacuate the regimental command post, threatened by tanks in Ćwiklice, and from there at the last moment infantry commander of the 6th Infantry Division, Col. Ignacy Misiąg, ordered the remaining battalions of the 20th Infantry Regiment and the 16th Infantry Division of the division’s reserve to a counterattack from their positions in the Brzeziny Forest.
Maj. Ludwik Bałos, commander of two battalions of the 20th Land of Kraków Infantry Regiment in Pszczyna, seeing the pointlessness of an infantry attack on tanks in open terrain, disobeyed the order. The commander of the 16th Infantry Regiment did just the opposite. His battalions lost about 300 soldiers, decimated by machine gun fire and crushed by tanks, which suffered only minor damage.
Having defeated the counterattacking Polish formations, the German tanks crossed Pszczynka and in the area of Jankowice attacked and destroyed most of the positions of the 6th Battery of Heavy Artillery, and the 6th Light Artillery Regiment’s 1st Battery; in the Jawiszowice area they reached an unprotected section of the Vistula and set about building a bridge.
In Pszczyna, behind the German forces, two 20th Land of Kraków Infantry Regiment Battalions and the remains of the 16th Infantry Division were still positioned. They blocked the road junction, cutting off the supply of fuel and ammunition for the tanks of the 5th Panzer Division. The shortages forced the Germans to stop the armoured advance and prompted two attempts to capture Pszczyna by motorized infantry supported by dive bomber attacks. Both of these attempts broke down in the fire of Polish infantry and mortars. The 9th company of Lt. Szoll, encircled at the left flank of the defense in Goczałkowice, held the position until 7.00 pm, then crossed the Vistula River at Dziedzice and departed towards Kęty. German publications recounting these battles praise the skill and courage of the defenders. Their authors have repeatedly written that individual heavy machine gun posts and anti-tank guns were firing in all directions right up until they were crushed by tracks, and the cannon crews, though blindsided in their unprotected positions, refused to leave until the very last moment, destroying many combat vehicles.
Col. Kazimierz Brożek, commander of the 20th Regiment, was cut off from his soldiers since the early morning. He had left for the division headquarters to receive orders, and didn’t manage to return in time. Worse still, neither the division staff nor the Army command had any contact with Pszczyna; their commanders decided that the 6th Infantry Division had essentially ceased to exist, and its defensive position had been breached. Orders were given to pull back towards Cracow and to blow up all bridges on the Vistula and Sola rivers, as well as on their tributaries.
After dark, the cut-off battalions of the 20th Infantry Regiment, along with their vehicles and carts, started their retreat by forest roads towards Chełmek. The 2nd battalion, while leaving its defensive positions, was fired at in an open terrain by saboteurs, and suffered significant losses. Having wandered all night, the Regiment’s elements reached the western bank of Gostynek in the village of Myrczek, expecting to find a bridge. It had been blown up the previous day, when the Kraków Army command received an exaggerated news from the commander of the 6th Infantry Division, reporting total destruction of his formation near Pszczyna. Within an hour and a half, a pioneer company rebuilt it so that the vehicles could cross the river. After a short rest, the retreat was resumed in the daylight. This time, the Luftwaffe limited itself to observing the marching troops, who reached the bridge on the Przemsza River around noon, when it was scheduled to be blown up. At the last moment, the river was crossed; only an infantry platoon of the rear guard was cut off and wiped out by German tanks.
After less than two hours of rest, the battalions resumed their march east towards Libiąż, where the 23rd Infantry Division was preparing the defense. In the afternoon and evening, the column marched on to the Bolęcin area, where it was ordered to rest and issued the first hot meal in two days.
At all times, the threat of attack hindered both marching and soldiers’ moments of rest.
On 4 September 1,500 men from the 20th Land of Kraków Infantry Regiment reached Kryspinów, awaited by Maj. Tadeusz Rybka with supplies from the Regiment's reserve storage point. The battalions marched through the city, first to Kobierzyn, then to Skotniki, Kostrz and Pychowice.
On 5 September, with the ranks of the 2nd and 3rd Battalions replenished, the Regiment returned to its full combat power and took part in repelling the German attack on Skawina. At night, following an order from General Antoni Szylling, the units left the defensive positions and went through Borek Fałęcki and Prokocim to the Niepołomicki Forest, towards the reserve forces of the 6th Infantry Division. The retreat continued the next night, and shortly after dawn, the bridge over the Raba river in the Ujście Solne area was crossed. The Raba line was not prepared for defense, which is why the army kept marching further east during the day. Around noon on 7 September, they stopped for rest in the Wał Ruda Forest, which was interrupted after only two hours by an order to march immediately towards the bridge in Biskupice Radłowskie. There, the 12th and 16th Infantry Divisions were to organize the defense of the Dunajec line, and the 20th Land of Kraków Infantry Regiment was ordered to move to the area of Dąbrowa Tarnowska and serve as a reserve formation. Unfortunately, marching was impossible, as the road was blocked by the vehicles of the 21st Mountain Infantry Division, which had been supposed to cross the Bobrowniki pontoon bridge, but had been pushed north by the Germans.
In these circumstances, Maj. L. Bałos decided that the Regiment would cross the river on foot, especially that according to the data he’d received, the bridge in Biskupice had been blown up. On the way to the crossing, however, he was informed by the commander of the 6th Light Artillery Regiment, Col. Kondracki, that the crossings near Otfinów and Nieciecza were not suitable for passage and that at dawn the 6th Infantry Division would attempt to recapture the bridge in Biskupice which, contrary to the earlier information, was in good condition but controlled by German tanks.
The darkness of the night and lack of communication prevented the exchange of information. On the one hand, an officer patrol of the 20th Land of Kraków Infantry Regiment learned from the residents of Biskupice that the bridge had in fact been blown up. On the other hand, the commander of the 3rd Podhale Rifle Regiment confirmed the news of the planned attack, but his unit was unable to gather in Wola Radłowska in time. Major L. Bałos decided that he would strike before dawn from the Zabawa farm area, taking the opportunity to surprise the enemy. The 1st battalion was to attack along the northern edge of the village, and its 1st company would reach the bridge to determine the actual condition of the structure. The 3rd battalion would mount a frontal attack on Biskupice on both sides of the road, and the 2nd battalion was to advance along the southern edge of the village up to the Szatanówka farm. The full-scale attack started at 4 am, but was soon stopped by the fire of guns and machine guns of tanks dug in on the approach to the village. On the flanks, where the German defense was weaker, some success was achieved. An attack was launched by the 3rd Podhale Rifle Regiment north of the village, and Szatanówka was entered from the south. It seemed that the capture of the entire region was close. However, the remaining units of the 6th Infantry Division had not launched an attack. Before dawn, they managed to find a good crossing point near Otfinów and, together with the 21st Mountain Infantry Division, left for Dunajec. In the gap, 50 German tanks of the 2nd Panzer Division charged from the direction of Radłów. The battle turned into a slaughter of Polish infantry. Lt. Wojciech Wielgus, the commander of the 6th company in Szatanówka, died with an anti-tank rifle, taken from a previously killed rifleman, in his hand, and his company was decimated. Lt. Bronisław Osmelak, the commander of the 4th company, died in the hamlet of Obryłka, together with several dozens of his soldiers. In all, the Regiment lost 243 dead and around 500 wounded.
During the most intense fights, Lieutenant Paweł Sawicki, the commander of the 1st Company, reported that he had reached the bridge. The structure, blown up and burned, was completely useless. This news could have led to a mental breakdown of the fighting soldiers, whose efforts and losses proved to be completely unnecessary. However, at the same time, a report arrived from Cpt. Władysław Krzystak, the commander of the 2nd Battery of the 21st Light Artillery Regiment, that Polish units had completed the crossing at Otfinow and that no further fighting with German forces was needed. The 20th Land of Kraków Infantry Regiment and 3rd Podhale Rifle Regiment could break away from the enemy and get to the other side of the river via the crossings in Konary, Nieciecza and Otfinow. The weakened Germans (who’d lost 19 tanks, 7 armoured cars and over 100 dead or seriously injured, including the unit commander, Col. Baumgart) were unable to pursue the retreating Poles. Only the Luftwaffe took an unsuccessful attempt to stop them, dropping a few bombs on the crossings.
On the morning of 8 September, Lieutenant J. Talaga and a patrol of the 20th Regiment’s communications unit ran into a German armoured scout detachment on the east bank of the river north of Biskupice. Under these circumstances, the Regiment did not attempt to defend the Dunajec line, but went far east, behind the San River. Along the way, on 9 September, they crossed Wisłoka on foot. On 10 and 11 September, they rested in the area of Zdziary. There, the remainder of the 4th Fortifications Battalion of Lieutenant Krawiec joined the Regiment. In addition, about 200 "survivors" from various units reinforced the 2nd and 3rd battalions. This allowed the Regiment to reach about half its full size, with 70% of weapons. On the morning of 12 September marching orders were received, and on this day, as well as on 13 September, the Regiment marched through Domostawy, Janów Lubelski, Momota and Huta Krzeszowicka to reach the banks of the river Tanew. Later they took part in the unsuccessful two-day assault of the 6th Infantry Division on Cieszanów, which was to clear the way for the "Boruta" Operational Group towards Lwów. On 16 September, the Regiment, along with the entire 6th Infantry Division, defended the Tanew line against the German 8th and 28th Panzer Divisions. The barrage from enemy artillery killed many soldiers, but the Germans failed to cross the river. At night, following fresh orders, the division departed to the Józefów area. The 20th Land of Kraków Infantry Regiment, as usual, formed the rear guard. On 17 September, it defended the Pardysówka area, and in a short but fierce battle its 1st battalion repelled a strong reconnaissance unit of the German 28th Panzer Division. That night, all of the Polish forces departed towards Tomaszów Lubelski, chased by artillery fire from the Nowin region. In the afternoon of 18 September, the 6th Infantry Division launched an assault on Narol. This time, the 20th Land of Kraków Infantry Regiment was to bring up the rear and move behind the advancing formations of the 12th and 16th Infantry Divisions, but soon had to support one of the 16th Infantry Division’s companies, and after two hours another company of the 12th Infantry Division fighting in Narol. The town was captured and in it a German field hospital, along with the wounded and a doctor. Polish wounded were placed there, and then the division moved towards Rawa Ruska. The 20th Land of Kraków Infantry Regiment made up the vanguard. On 19 September in Werchrat it enveloped and took prisoner soldiers of a construction unit, and destroyed a transport of vehicles at the local railway station. All the following day they marched southwest. The Regiment was under the constant surveillance of German reconnaissance planes – Polish aircraft were absent from the sky.
On 20 September 1939, before noon, a German negotiator called for the surrender of the 6th Infantry Division. General Bernard Mond ordered an officers’ briefing. The regiment commanders reported that the soldiers were exhausted from marches and battles, food was in short supply, only a few rifle cartridges remained, the artillery was out of shells, medical personnel had run out of bandages and the wounded were starting to die. Considering all this, the division commander decided to take the responsibility and surrender. He also released officers and soldiers from the obligation to enter into captivity. They could hide in the woods and try to leave Poland or continue to fight in the country.
The 20th Land of Kraków Infantry Regiment was disbanded. For their heroism in battle, 17 officers, 8 non-commissioned officers and 5 riflemen were presented for decoration with the Virtuti Militari Cross by the Regiment commander; further 31 officers, 23 non-commissioned officers and 11 riflemen were awarded the Cross of Valour. During the campaign, the Regiment destroyed 64 and damaged 19 enemy armoured vehicles.