On 22 June 1941, the 17th Army was part of Army Group South when Nazi Germany launched Operation Barbarossa and invaded the Soviet Union. From 1 July, the Hungarian "Mobile Corps" ("Gyorshadtest") was subordinated to the 17th Army. Along with 1st Panzer Army, the 17th Army encircled Soviet forces in central Ukraine during the Battle of Uman. Approximately 100,000 Soviet troops were captured. The 17th Army participated in the Battle of Kiev. Army Group South was ordered to resume the offensive, with the objective of capturing Rostov-on-Don, the gateway to the Caucasus oil fields, and Kharkov, a major center of heavy industry for the Soviet Union.