Kühn and the 14th Panzer Division participated in Operation Barbarossa as part of 1st Panzer Group under Army Group South, crossing into Russia near Ustyluh on 20 June 1941. The division captured Lutsk on 26 June 1941, reached Rivne by 1 July, and Bila Tserkva by 23 July 1941. The division turned south and drove through Uman on to Kirovohrad, which fell on 5 August 1941. Kühn then led the division through Kryvyi Rih to participate in the fight for Dnipropetrovsk, which lasted until 10 September 1941. The division then turned south and participated in the Battle of Rostov (1941), before spending the winter in defensive positions around the Mius River.