At the start of Operation Barbarossa, the division passed under the operational command of the XIth Corps Wehrmacht's 11th Army, led by General Eugen Ritter von Schobert. Romania joined Operation Barbarossa on 22 June in order to reclaim the lost territories of Bessarabia and Northern Bukovina, which had been annexed by the Soviet Union in June 1940. Sion crossed the Prut River with the 1st Armored Division during the night of July 2/3, at the start of Operation München. After an engagement with the Red Army at Brătușeni, his troops advanced towards the Dniester River, first in the direction of Mohyliv-Podilskyi, then towards Soroca and Bălți, and then playing a decisive role in the occupation of Chișinău on July 16. On 5 August the 1st Armored Division was put under the operational command of the Romanian 5th Corps. That night, the division crossed the Dniester, and then served as the lead unit of the Romanian 4th Army (under the command of General Nicolae Ciupercă) in its advance towards Odessa, reaching the outskirts of the city by August 14. After a disastrous attack on 18 August on the Karpova railway station (where the Soviets had dug in along the railbed embankments), Sion was relieved of his command by Marshal Ion Antonescu and replaced by General . He returned to the command of the 1st Armored Division on October 10, and kept the position until January 10, 1942, when General took over, with Sion as second in command.