The 'Battle of Tomaszów Lubelski' was fought between German and Polish forces near the town of Tomaszów Lubelski within the context of the 'Weiss' (i) German invasion of Poland, was the second largest battle of that campaign after the 'Battle of the Bzura', was also the largest tank battle of the campaign and led to the surrender on 20 September of the Armia 'Kraków' (17/26 September 1939).

The battle was fought in two phases on 19/20 September and 21/26 September.

In the first phase, which is sometimes known as the 1^st Battle of Tomaszów Lubelski, the Polish forces of Generał dywizji Tadeusz Piskor’s Armia 'Lublin' and Generał dywizji Antoni Szylling’s Armia 'Kraków' attempted to break through the German positions around Tomaszów toward the Romanian 'bridgehead' area. On 15 September the forces of both armies were in the area to the south-west of Frampol, but their axis of retreat to the south was was blocked by two German formations, namely General Ernst Buisch’s VIII Corps in the area round Biłgoraj and General Ewald von Kleist’s XXII Corps (mot.), comprising Generalleutnant Rudolf Veiel’s 2^nd Panzerdivision and Generalleutnant Dr Alfred Ritter von Hubicki’s 4^th leichte Division in the area round Hrubieszów, Zamość and Tomaszów Lubelski. Thus the Polish forces, concentrated around Frampol, were surrounded by six to seven German divisions. Since neither the Armia 'Kraków' nor the Armia 'Lublin' had air support, Szylling decided to take the risk of attacking the Germans without knowing their real strength. What Szylling did know was that the German armoured forces were already near Rawa Ruska, but he hoped that their units would be stretched along the road between Jarosław ando Rawa.

The Polish forces included one of the largest Polish armoured units of the period, namely Generał brygady Stefan Rowecki’s Warsaw Armoured Motorised Brigade, and Szyling and Piskor together decided that this brigade would make a demonstration attack on Tomaszów, drawing the attention of the Germans to that sector. The combined forces of the two Polish armies comprised five infantry divisions in the form of the 3^rd, 21^st, 22^nd, 23^rd, and 55^th Divisions. Furthermore, they also had the 1^st Mountain Brigade, the Kraków Cavalry Brigade and, of course, the Warsaw Armoured Motorised Brigade. However, after days of heavy fighting, all these Polish formations and units except the Warsaw Armoured Motorised Brigade had been reduced to between one third and one half of their original strength in men, and were also short of essential supplies including anti-tank ammunition.

The Polish plan was soon changed, however, after the Germans had destroyed key Polish formation, the 21^st Mountain Division, near the village of Dzikowiec, on 15/16 September; the divisional commander, Generał brygady Józef Kustroń, was killed. Now realising that the German forces were stronger than he had first believed, Piskor now decided to act quickly, without waiting for all his divisions to concentrate. On 17 September he ordered the Warsaw Armoured Motorised Brigade to attack Tomaszów and hold this town until the main forces of the Armia 'Kraków' arrived to supplement the brigade. Tomaszów was attacked during the morning of 18 September, and by 13.00 half of the town was in Polish hands. Meanwhile, however, the 4^th leichte Division had joined the battle, striking rear Polish units and forcing them to withdraw. Thus, the surprise-attack attempt to take Tomaszów failed. During the night of 18/19 September, the Warsaw Armoured Mechanised Brigade, supported by the infantry of the 23^rd and 55^th Divisions, attacked Tomaszów again, but without success. A third attack took place during the night of 19/20 September, but by this time the Polish units were both disorganised and demoralised, and after a series of chaotic skirmishes, and with the number of killed and wounded growing, and ammunition quantities shrinking, Piskor decided to surrender. Some 11,000 Polish soldiers were taken prisoner, but small groups managed to hide in forests.

Meanwhile, the Operational Group 'Boruta' commanded by Generał brygady Mieczysław Boruta-Spiechowicz and an element of the Armia 'Kraków', split away from main Polish grouping and marched toward Narol. Surrounded by Germans, Polish formations and units were destroyed on a piecemeal basis. Some managed to reach the area of Rawa Ruska, where 3,000 men surrendered on 20 September, so ending this first phase of the battle.

The second phase, sometimes known as the '2^nd Battle of Tomaszów Lubelski', involved Polish formations and units of Generał dywizji Stefan Dąb-Biernacki’s so-called Northern Front: these were the remnants of the Armia 'Lublin', the Armia 'Modlin', the Operational Groups 'Wyszków' and 'Narew', and the Nowogródzka Cavalry Brigade under Generał brygady Emil Krukowicz-Przedrzymirski and Dąb-Biernacki. On 20 September these forces were some 25 miles (40 km) to the north of Tomaszów, in the area of Sitaniec. Dąb-Biernacki, who was in overall command, had no idea until the final hours about the ongoing battle and could not help the fighting troops. At the same time, Piskor did not know about Dąb-Biernacki’s formations and units operating to the north-east of Tomaszów. The Northern Front had some 39,000 men and 225 pieces of artillery, and was divided into three groups, namely Generał brygady Władysław Anders’s Cavalry Operational Group 'Anders', Generał brygady Jan Kruszewski’s Operational Group 'Kruszewski' and Krukowicz-Przedrzymirski’s Operational Group 'Krukowicz-Przedrzymirski'. The Polish forces were in no way any real match for General Walter von Reichenau’s 10^th Army and General Wilhelm List’s 14^th Army of Generaloberst Gerd von Rundstedt’s Heeresgruppe 'Süd' holding the roads to the south, but at a meeting of his officers on 18 September in the village of Wereszcze Duże near Chełm, Dąb-Biernacki decided to go along with an attempt to break out into Hungary or Romania. Dąb-Biernacki already knew that Soviet forces had invaded eastern Poland on the previous day, so time was of crucial importance.

The Northern Front’s forces marched to the south from the area of Chełm in two columns toward Zamość, which Dąb-Biernacki decided to attack. On 18 September the Poles attacked Krasnystaw, but failed to capture it. On the next day, Dąb-Biernacki ordered an attack on Zamość on 20 September, but on the night of 19/20 September learned of the ongoing 'Battle of Tomaszów Lubelski' and decided to help. The Northern Front’s formations and units headed toward Tomaszów, but during the evening of 20 September were themselves attacked by the 4^th leichte Division and Generalleutnant Friedrich Bergmann’s 27^th Division in the area of Cześniki. Meanwhile, units of the Operational Group 'Krukowicz-Przedrzymirski' reached the area of Tomaszów, and on 21 September, only a few hours after the first phase of the battle had ended, attacked troops under Busch’s command, namely Generalleutnant Rudolf Koch-Erpach’s 8^th Division and Generalleutnant Hans von Obstfelder’s 28^th Division. Since the Polish forces proved to be stronger than expected, List decided to send reinforcements to Busch: these were Generalleutnant Georg Braun’s 68^th Division, Bergmann’s 27^th Division and Veiel’s 2^nd Panzerdivision, which had just completed the mopping up of the Polish forces at the end of the first phase of the 'Battle of Tomaszów Lubelski'.

During the evening of 22 September, cavalry of the Operational Group 'Anders' attacked, capturing Krasnystaw and then reaching Sambor. Other Polish units were not successful, and in several skirmishes were surrounded on 23 September. Dąb-Biernacki ordered his officers to capitulate, but himself escaped the encirclement and left Poland to reach France. Przedrzymirski refused to obey the order, and on 24 September attacked Krasnobród only to be stopped by the 8^th Division. Most of the remaining Polish forces capitulated on or around 26 September.