The final major campaign in which the Panzer I formed a large portion of the armoured strength was "Operation Barbarossa", 22 June 1941. The 3,300 German tanks included about 410 Panzer I's. By the end of the month, a large portion of the Red Army found itself trapped in the Minsk pocket, and by 21 September Kiev had fallen, thereby allowing the Germans to concentrate on their ultimate objective, Moscow. Despite the success of Germany's armour in the Soviet Union, between June and September most German officers were shocked to find their tanks were inferior to newer Soviet models, the T-34 and KV series. As seen during the Spanish Civil War only 5 years earlier, the Panzer I was clearly no match for even the weakest of Soviet armour it encountered, with even armoured cars such as the BA-10 proving capable of defeating the Panzer I when fitted with medium-caliber anti-tank weapons. Army Group North quickly realized that none of the tank guns currently in use by German armor could reliably penetrate the thick frontal armour of the KV-1. The performance of the Red Army during the Battle of Moscow and the growing numbers of new Soviet tanks made it obvious the Panzer I was not largely suitable for this front of war. Some less battle-worthy Panzer Is were tasked with towing lorries and other light (mainly wheeled) vehicles through the thick Russian-autumn mud to alleviate logistical and transportation issues and problems at the frontlines, whilst other Panzer Is were relegated for anti-partisan actions or rear-guard protection duties (such as defending airfields or other vital military installations on occupied enemy territory).