 After General ( later Marshal ) Ion Antonescu took power in September 1940 , Romania signed the <unk> Pact with the Axis Powers and subsequently took part in Operation Barbarossa in 1941 . An expeditionary force invaded the Soviet Union in <unk> and southern Ukraine , alongside the German Wehrmacht . The expeditionary force , ' Army Group Antonescu , ' was composed on 22 June 1941 of the 3rd Army , the 4th Army , the 2nd Army Corps , and the 11th Infantry Division . The 3rd Army comprised the 4th Army Corps ( 6th and 7th Infantry Divisions ) , the Cavalry Corps , the Mountain Corps , two separate artillery battalion , a TA unit , and the Air Force 's 3rd Army Cooperation Command . The 4th Army consisted of the 3rd Army Corps , the 5th Army Corps , the 11th Army Corps ( two fortress brigades ) , and the 4th Army Cooperation Command . The army group @-@ level 2nd Army Corps , under Major General N. <unk> , controlled the 9th and 10th Infantry Divisions and the 7th Cavalry Brigade . Additionally the 1st Armoured Division was formed for service on the Eastern Front . The Army Group 's first offensive , in conjunction with the <unk> Army , Operation <unk> , enabled Romania to retake the territory immediately east of the <unk> , former part of Moldavia . The Romanian Armies saw their first major battles at Odessa and Sevastopol , and in 1942 advanced with other Axis forces deeper into Soviet territory during Operation Blue . 
