By 15 September, German forces including the 1st and 2nd Panzer Groups had completed the largest encirclement in history, the Battle of Kiev. Owing to the 2nd Panzer Group's southward turn during the battle, the Wehrmacht destroyed the entire Southwestern Front east of Kiev, inflicting over 600,000 losses on the Red Army by 26 September. However, the campaign had been costly; the German forces had just half the tanks they had three months earlier. They were bogged down in a war of attrition for which the Wehrmacht was not prepared. Guderian's 2nd Panzer Group was in the worst shape; it had just 21 per cent of its tanks in working order. In mid-September, he was ordered to make a drive for Moscow. On 30 September the Battle of Moscow began. On 4 October, the 4th Panzer Division, part of the 2nd Panzer Group suffered a severe setback at Mtsensk, near Oryol. Guderian demanded an inquiry into the realities of tank warfare on the Eastern Front, eventually suggesting in November to senior German tank designers and manufacturers that the quickest solution was to produce a direct copy of the Soviet T-34 tank.