After bringing into light the Katyn massacre and breaking off the diplomatic relations with Poland (April 1943), Stalin decided to organize Polish armed forces fighting at side of the Red Army. These troops emerged without the approval of the legal authorities of Poland, most of the commanding personnel were Soviet officers, the political officers recruited from the Polish communists but ordinary soldiers were Poles deported in the years 1939-1941 to the interior of the Soviet Union, and from the spring 1944, also the inhabitants of the Polish Kresy Wschodnie (Eastern Borderlands). Though its origin was not legal, and it played a significant role in imposing the communist system in Poland later on, the Polish Army fighting on the Eastern Front contributed a lot to the Polish military effort. From a single division (1st Tadeusz Kościuszko Infantry Division, commanded by colonel Zygmunt Berling) eleven-thousand-people strong, which began to form in May 1943, it expanded to one-hundred-thousand-people-strong army in July 1944, and at the end of the war it amounted to more than 330 thousand soldiers formed in two armies with all land forces arms (infantry, artillery, engineers, tanks and different supporting troops).
This army’s baptism of fire took place at the battle of Lenino (Belarus) in October 1943. In July and August 1944 the Polish troops fought at the bridgeheads on the Western Bank of the Vistula River, and in the battle of Studzianki the Polish armored brigade fought its first battle against the Germans. In September 1944 the Polish Army attempted at helping the insurgents in Warsaw – unsuccessfully and with great losses. From January 1945 it participated in the great Soviet offensive: in February and March it fought a dramatic battle to break the Wał Pomorski (Pomeranian Position – the highly fortified German defense line) and capturing Kołobrzeg (Kolberg), a Baltic seaport transformed into a fortress; the Polish troops fought at Gdańsk and Gdynia, and also by Zalew Szczeciński (Bay of Szczecin). The crowning of the combat route was participation in capturing Berlin. In the entire operation took part 180 000 soldiers from the 1st and 2nd Polish Army, and in the assault in the downtown of Berlin an important role played the 1st Tadeusz Kościuszko Division. It was the only military unit besides the Red Army that stuck its national flag over the ruins of the German capital. Polish troops reached the Elba River and got in touch with American units. In April 1945, the 2nd Army forced the Nysa River, then fought in the region of Dresden and Bautzen, suffering great losses. Its combat route it ended in May in Czechoslovakia. In battles against the Germans on the Eastern Front participated also some Polish air units (however, they consisted mainly of Soviet pilots).
From the battle of Lenino till the combat over Elba and in Saxony 17 500 soldiers were killed, almost 10 000 were considered to be MIA. The most casualties cost the fighting in Pomorze (Pomerania – 5400 killed and 2800 MIA) and in the Berlin operation (7200 killed and 3800 MIA). Because of the combined nature of the Soviet and Polish actions it is difficult to estimate how much damage the Poles inflicted to the enemy. Some partial data is available only for a few battles: at Lenino 1800 Germans were killed, wounded or taken prisoner, in the tank battle at Studzianki the Germans lost 20 tanks and self-propelled guns and 1500 soldiers, at Wał Pomorski 2300 killed. In Berlin the soldiers of the Kościuszko Division captured four subway stations and took prisoner 2500 German soldiers.
The Polish Army fighting in the East was the greatest regular military force fighting at the side of the Red Army. Its combat route lasted for almost two years, adding up to 1000 kilometers. It participated in different and important activities: forcing rivers, capturing cities, attacking fortifications, pursuing enemy troops. Its share in victory was paid dearly.