Initially formed in March 1941, in response to the German victories in the West it was attached to the newly forming 27th Army, and held in reserve near Opochka in Soviet Union 130 kilometres (81 mi) South of Pskov[1] in the Special Baltic Military District.

[2] a After the Invasion began the Special Baltic Military District was renamed Northwestern Front, Commanded by Colonel General Kutznetsov.

After the spectacular advances by 4th Panzer Group Kutznetsov asked Stavka for the release of Berzarin's 27th Army and the 21st Mechanized Corps on 25 June and was ordered to halt Erich von Manstein's LVI Panzer Corps which was closing up to the Daugava River later that day both units engaged near Dvinsk.

Next Army Group North sent a special force which captured the bridges at Daugavpils and consolidated with 8th Panzer Division.

[3][4]b After continuing a fighting retreat through the Baltic states in July, but in remnants the 21st Mechanized Corps was disbanded in August 1941.