The 'Battle of Mokra' was a battle between German and Polish troops near the village of Mokra, 3.1 miles (5 km) to the north from Kłobuck and 14.3 miles (23 km) to the north-west of Częstochowa within the context of the 'Weiss' (i) German invasion of Poland (1 September 1939).

The battle was one of the first during the invasion of Poland, ands also one of the few Polish victories of that campaign as well as the first German defeat of the conflict.

In accord with the Polish main mobilisation plan, the primary task of Generał dywizji Juliusz Rómmel’s Armia 'Łódź' was to secure the overland link between Generał dywizji Antoni Szylling’s Armia 'Kraków' operating in Silesia and Lesser Poland and Generał dywizji Tadeusz Kutrzeba’s Armia 'Poznań' defending Greater Poland. It was also to cover the mobilization of a reserve formation, Generał dywizji Stefan Dąb-Biernacki’s Armia 'Prusy', behind the Polish front lines. Because of that, the army’s primary main purpose was to buy time by undertaking delaying actions and offering severe resistance in order for the mobilisation to be accomplished.

Pułkownik Julian Filipowicz’s 'Wołyńska' Cavalry Brigade was located to the north of Kłobuck, along the railway line to Katowice. The 19^th 'Volhynia' Uhlan Regiment, 21^st 'Vistula' Uhlan Regiment and 4/84^th Regiment were entrenched on both ends of the forest in which lies the village of Mokra, to the west of the north/south railway. To the east, Filipowicz placed the brigade’s reserves, namely the 12^th 'Podolian' Uhlan Regiment, the 2^nd Mounted Rifles Regiment and the 21^st Armoured Battalion. The main task of the Polish brigade was to maintain the physical link between the 7^th Division operating to the south and the 30^th Division to the north. The terrain chosen by the Polish commander was ideal for defence: a raised railway embankment and a forest formed the main defensive line, while the area in from of these was hilly and cut by a large number of ditches, streams and other obstacles.

At 05.00 on 1 September, General Walter von Reichenau’s 10^th Army of Generaloberst Fedor von Bock’s Heeresgruppe 'Nord' crossed the border into Poland as the first step in 'Weiss' (i). Generalleutnant Rudolf Kaempfe’s 31^st Division, as well as Generalleutnant Rudolf Schmidt’s 1^st Panzerdivision and Generalmajor Georg-Hans Reinhardt’s 4^th Panzerdivision crossed the border in the sector of the 'Wołyńska' Cavalry Brigade. After breaking through small border guard and national defence detachments, the German formations seized the towns of Krzepice and Starokrzepice directly in front of the main Polish positions. After capturing these towns, the Germans razed both of them and expelled all the local inhabitants toward the Polish lines.

The German formations were operating as three separate assault groups. The 1^st Panzerdivision headed directly toward the town of Kłobuck, held by the 7^th Division, while the 4^th Panzerdivision was split into northern and southern columns, each trying to outflank the Polish positions around Mokra. At the same time, the Luftwaffe began a heavy bombardment of the Polish positions. By the end of the day, German aircraft, of which most were Junkers Ju 87 tactical dive-bombers, had flown 15 missions with between nine and 26 bombers in each.

At 06.0 the motorcycle reconnaissance teams of the 4^th Panzerdivision's 34^th Kradschützenbataillon made contact with the 12^th Company of Podpułkownik Stanisław Radajewicz’s 84^th Regiment, and soon after this the German armour arrived, supported by infantry and purportedly using Polish civilians as human shields. However, after several hits from Polish anti-tank weapons on their flanks, the German tanks lost orientation, which allowed the civilians to cross the Polish lines with negligible losses. Soon after this, the Germans renewed their assault, but this was repelled by heavy machine gun fire. Two tanks fell back, and most of the motorcyclists were taken prisoner.

The 4^th Panzerdivision then began an assault on the 21^st Uhlan Regiment slightly farther to the north. After a short artillery barrage and aerial bombardment, the German tanks took the village of Wilkowieck and headed directly for the village of Mokra. Although it lost many horses and about five ammunition carts, the Polish cavalry regiment was largely missed by the bombing, and from it defensive positions gave the German tanks a sharp welcome at a range of 165 yards (150 m) by its well-sited Polish-made 37-mm Bofors anti-tank guns. After two of their number had been destroyed, the rest of the German tanks withdrew to a distance of 440 yards (400 m) and started to use their main guns on the Polish positions. However, after losing two more of their tanks (one destroyed and one immobilised), the German tanks retreated. The German infantry were left on a flat open field, straight ahead of the Polish positions and without any cover. Thus the infantry units were compelled to retreat by a Polish infantry attack that caused heavy losses and resulted in a number of prisoners being taken by the Poles.

The positions of the 19^th Uhlan Regiment were attacked at 08.00 by an assault group of tanks, other armoured fighting vehicles, motorcyclists and infantry. The German group, divided into three columns, was advancing toward the village of Rębielice Szlacheckie in order to outflank the 21^st Regiment from the north. However, the Germans were apparently unaware of the 19^th Regiment’s positions. While the most westerly group took the village with ease, the central group was caught in an ambush by the Poles near the forest and was driven back in disorder. The third group was advancing toward the Polish positions in the forest, completely unaware of the Polish force several hundred metres away. When the Polish machine guns and anti-tank guns opened fire, the group was almost annihilated before it could respond.

Nevertheless, the Polish northern flank was endangered and the Germans now know its dispositions. To counter the threat, Filipowicz ordered the 12^th Uhlan Regiment, until then held in reserve, to strengthen the positions of the 19^th Regiment. The newly arrived unit was fresh, yet already battle-experienced in the first skirmishes in the early morning, which helped Polish morale.

At 10.00, the Germans launched an assault on the Poles' northern flank, but were checked in front of most positions with significant losses on both sides. Some 15 minutes later, the 4^th Panzerdivision repeated the attack, this time with artillery support and air cover. The assault was planned in three directions: toward the positions of the 19^th Regiment and farther to the north, in order to outflank the brigade; toward the village of Mokra itself using some 100 tanks and other armoured fighting vehicles; and toward the weakened 4/84^th Regiment.

The northern assault was carried out quickly. Under heavy covering fire, the German tanks, which were a mix of PzKpfw I and PzKpfw II machines, managed to break into the forest and secure a road leading across the railway line to the village of Izbiska Duże, to the north of the Polish headquarters. At 10.30, the Polish 4^th Squadron of the dismounted 19^th Cavalry Regiment was attacked from the rear and pushed out of the forest. This threatened to divide the 19^th and 21^st Regiments, so Filipowicz ordered the 19^th Regiment to withdraw to the other side of the railway, but this route was already held by German tanks and the unit was effectively surrounded. However, the Polish defence was reinforced by the No. 53 armoured train, known as Śmiały (bold), which arrived on the battlefield just as the German tanks were crossing the railway line. The train halted in the middle of the German column and opened fire on the German tanks at close range with its two 75-mm (2.95-in) guns and heavy machine guns. The German column was dispersed and retreated with heavy losses, losing a number of its PzKpfw I and PzKpfw II tanks, while the 19^th Regiment crossed the railway under cover of the armoured train' fire. Although the 19^th Regiment suffered heavy losses, it managed to regroup on the other side of the railway line.

Simultaneously, a German attack began on the main positions of the 21^st Regiment near the village of Mokra. German tanks outflanked the 4^th Squadron of the 21^st Regiment from the north, at the same time attacking it frontally. The Polish defenders were pushed out of the forest, and there began heavy fighting for the village. The Germans lost four tanks to the 2^nd Artillery Battalion firing from across the railway, but the 4^th Squadron was still in retreat, fighting for almost every house in the village and suffering heavy losses. Again the day was saved by Śmiały, which arrived at the height of the battle and opened fire from a range of little less that 2,735 yards (2500 m), which was beyond the effective range of all German tank guns of the time, in the end destroying or knocking out several more PzKpfw I and PzKpfw II machines. Additionally, more Polish cavalry, of the 12^th Uhlan Regiment, arrived in the area: the men dismounted and reinforced the 21^st Regiment.

Major Stanisław Gliński’s 21^st Armoured Battalion, equipped mostly with TKS tankettes, was ordered to counterattack the village, along with Kapitan Jerzy Hollak’s cavalry squadron. In the billowing smoke of the burning village, the Polish units inadvertently drove straight into the middle of a German tank column. Although the Polish tankettes were no match for the heavier PzKpfw II machines and the cavalry was very vulnerable to tank fire, confusion in the German ranks prevented their commander from responding quickly enough. The Polish units managed to break through the German column with negligible losses and seized the forest to the north-west of Mokra. This manoeuvre has sometimes been referenced as a Polish cavalry charge against German tanks, but a charge was neither planned nor executed. Nevertheless, the German tanks again lost orientation and the column withdrew from the village, again leaving it in Polish hands. The tanks withdrew to their initial positions in Wilkowiecko, leaving behind the infantry supporting the failed assault. German losses were considerable and a large number of Germans were taken prisoner.

Also at 10.00, the positions of the 4/84^th Regiment were attacked by a detachment of German mechanised infantry. After initial clashes, the Polish 11^th and 12^th Companies withdrew deeper into the forest. Filipowicz ordered the 2^nd Mounted Rifles to counterattack and strengthen the positions between the 21^st and 84^th Regiments. Additionally, the 10^th Company charged the Germans and retook the positions lost only a short time earlier. By 12.00, the fighting in the centre and south of the Polish positions was over, and the fighting in the forest on the northern flank ended after the 19^th Regiment had effected a successful withdrawal.

At 12.15 a force of about 100 German tanks returned to the village of Mokra. The main assault broke the lines of the 21^st Regiment’s 4^th Squadron, and the tanks charged the anti-tank artillery nests, destroying two of the guns and breaking through to the central part of the village, where the houses were set on fire. The 21^st Regiment managed to withdraw to the railway line under cover of the smoke. Only isolated pockets of resistance were left in the village, which caused much confusion to the Germans.

The withdrawal of the 21^st Regiment allowed the Germans to make a direct attack on the 12^th Regiment and the 2^nd Artillery Battalion. The latter’s losses were high since most of its 75-mm (2.95-in) field guns were not well-suited to the anti-tank role. The 2^nd Battery lost all three of its guns and the heavy machine gun, while the 5^th Battery lost two guns. The rest of the artillery positions were covered by smoke from the houses the Germans had set on fire, however, and were thus hidden from view. When a group of tanks unknowingly approached the 1^st Battery, the Polish opened direct fire on the German tanks, destroying 13 of them in a matter of minutes and making it possible for the Poles to hold their positions. The 12^th Regiment attacked the German tanks from the rear out of the recently retaken forest to the north-west of the village. Although both sides suffered heavy losses, the Germans withdrew. After the assault had ended, the 2^nd Artillery Battalion was withdrawn from the battle as a result of its heavy losses and lack of ammunition.

At 15.00, the Germans repeated their frontal assault from Wilkowiecko with the support of heavy artillery fire, tactical air attacks and almost 180 tanks. Simultaneously, attacks were made on the Polish flanks. The frontal assault was directed at the 12^th Regiment’s 2^nd Squadron in the centre of the village. Although the Polish artillery destroyed many of them, the German tanks managed to break through once again to the village. The 4^th Squadron counterattacked, but both squadrons were under constant pressure toward the railway line. Filipowicz had no further reserves and the German tanks were nearing the railway crossing, while the Polish cavalry was being pushed back with heavy losses. The regiments soon lost contact with each other. As a result of the smoke, the battle broke down to a series of skirmishes in the forests, the village and along the railway line. All but one of the 2^nd Battalion’s batteries were withdrawn, and this left the situation of the 12^th Regiment critical.

The 2^nd Mounted Rifle Regiment, the only unit that was still intact and in contact with the brigade commander, was now instructed to assault regardless of cost and reinforce the 12^th Regiment and the gap between the cavalry and the 84^th Regiment in the south. This helped the Polish defence, but only for the moment. Filipowicz ordered the Polish tankettes to attack the German tanks in the village. Although possessing no anti-tank ammunition, in the chaos of the battle the tankettes managed to halt the German advance, albeit temporarily. After losing one tankette the Poles withdrew, but managed to gain enough time for the two armoured trains to return to the area. To the north, at the positions of the 19^th Regiment the tanks also managed to break through and started to cross the railway near Izbiska. When the German tanks crossed the line, both of the armoured trains arrived and attacked them from the rear. While the tank losses were limited, the disorganisation that emerged in the German units resulted in many tanks being abandoned by their crews, who could not drive their tanks straight over the railway line as this was carried by an embankment some 6.7 ft (2 m) above the ground; the crossing was also blocked by burning armoured fighting vehicles. Although both trains suffered some losses and were finally forced to retreat, this did not immediately halt the panic in German ranks, and in the smoke some of the German tanks started firing on German positions, while others retreated toward their initial position, directly through the German infantry.

In the south the Polish infantry was yet again pushed deeper into the forest, but its lines were not broken. By 17.00 the battle was over.

The 4^th Panzerdivision had to pull back to its initial positions in Opatów and Wilkowiecko, and only the 12^th Schützenregiment managed to reach the railway crossing at Izbiska. However, upon learning that the 1^st Panzerdivision had taken Kłobuck, the Polish forces were withdrawn to the south-east during night to the village of Łobodno located to the north-east of Kłobuck, and then to the second line of defence, some 7.5 miles (12 km) farther to the east.

The losses on both sides were quite high. The Germans lost about 800 men killed, captured, wounded or missing, and between 100 and 160 armoured fighting vehicles including at least 50 tanks. The Polish brigade lost 200 men killed and 300 wounded, as well as 300 horses and several pieces of artillery. The 2^nd Mounted Artillery Battalion lost almost one-third of its men, the 21^st Regiment almost one quarter, and the the 12^th Regiment, which had been used as a reserve, lost five officers and 216 men killed and wounded.