In June 1941 with the launching of Operation Barbarossa, Kleist led the 1st Panzer Group as part of Army Group South - tasked with the capture of Moldavia and Ukraine - and saw success in the initial phase of the invasion, advancing deep into Ukraine. The 1st Panzer Group broke through the Stalin Line, then defeated the five mechanized corps of the Soviet 5th Army and 6th Army in the Battle of Brody (23 to 30 June 1941). In July 1941 during the Battle of Uman, the 1st Panzer Group broke through the Soviet Southern Front's lines, leading to the encirclement and annihilation of the Soviet 6th and 12th armies to the southeast of Uman city (in present-day Cherkasy Oblast). During the First Battle of Kiev of August–September 1941, 1st Panzer Group's northward turn from central Ukraine in conjunction with 2nd Panzer Group's southward advance from Smolensk led to the encirclement and destruction of the entire Soviet Southwestern Front east of Kiev, inflicting over 600,000 losses on the Red Army. However, the campaign had been costly, by then the German forces had just half the tanks they had had three months earlier.