Till October 1944, the First Army was commanded by Lt. Gen. Zygmunt Berling. His second-in-command was Lt. Gen. Karol Świerczewski. Włodzimierz Sokorski was the chief political officer. The corps took part in combat from September 1943. It operated under the auspices of the Red Army. It first entered combat in the summer of 1944 as part of the 1st Belorussian Front on the right wing of the Lvov-Sandomierz Operation, fighting in the battles during the Soviet crossing of the river Vistula around Dęblin and Puławy. In September 1944 units of the First Army were involved in heavy fighting during the latter stages of the Warsaw Uprising after crossing the river Vistula following the capture of Warsaw's eastern Praga district, but suffered heavy losses. After eventually taking control of Warsaw in January 1945, the First Army took part in the Vistula–Oder Offensive, and afterwards it moved towards Bydgoszcz. The Polish First Army then fought in Pomerania, breaking through the Pomeranian Wall ("Pommernstellung") fortified line and capturing Fortress Kolberg, a heavily fortified city, in March. Its units advanced northeast as far as Gdańsk and Kępa Oksywska. During the battles to penetrate the Pomeranian fortifications, the 1st "Warsaw" Cavalry Brigade made the last mounted charge of Polish cavalry at the village of Schoenfeld. In the spring of 1945 the army, now numbering 78,556 soldiers, was redeployed to the front on the Oder river in preparation for the final Soviet offensive of the war in Europe. The Polish Second Army also entered the line of battle at this time, and together the two armies contributed about 10% of the total forces involved in the operation. During the offensive it crossed the river on April 16 and joined the Battle of Berlin. In it, among other actions, Polish units of the 1st Army crossed the Hohenzollern Canal and advanced on Kremmen, Flatow, Paaren and Nauen. They ended their campaign by participating in the Battle of Berlin. In the Berlin Offensive, the First Polish Army's strength was over 74,000, thus making up 7.5% of the strength of the Soviet 1st Belorussian Front, which counted over 980,000 men when the Polish First Army is included in the total.