Łódź Army was one of the Polish armies of the Polish Armed Forces of the Second Polish Republic that took part in the Invasion of Poland of 1939. It was officially created on 23 March 1939 with the task of filling the gap between Poznań Army in the north and Kraków Army in the south. Commanded by Juliusz Rómmel, it consisted of five infantry divisions and two cavalry brigades with support from the air force.

Kraków Army was one of the Polish armies which took part in the Polish Defensive War of 1939. It was officially created on March 23, 1939 as the main pivot of Polish defence. It was commanded by Gen. Antoni Szylling. Originally, Kraków Army was to be made of seven infantry divisions, two cavalry brigades and one mountain brigade. On September 1, 1939, General Szylling had the force which consisted of five infantry divisions, two cavalry brigades and one brigade of mountain infantry. Altogether, the army was made of 59 battalions, 29 squadrons, 352 cannons, 90 tanks, two armoured trains and 44 planes. These forces were not enough to halt German advance, especially in the area north of Częstochowa, where Kraków Army connected with Łódź Army. Main thrust of Wehrmacht panzer units was directed there, and this area was defended only by the Polish 7th I.D., which was destroyed in the early days of September 1939, opening the way towards central Poland.