 Four weeks into the campaign , the Germans realized they had grossly underestimated Soviet strength . The German troops had used their initial supplies without attaining the expected strategic freedom of movement . Operations were now slowed down to allow for resupply ; the delay was to be used to adapt strategy to the new situation . Hitler by now had lost faith in battles of encirclement as large numbers of Soviet soldiers had escaped the pincers . He now believed he could defeat the Soviets by economic damage , depriving them of the industrial capacity to continue the war . That meant seizing the industrial center of Kharkov , the Donbass and the oil fields of the Caucasus in the south and the speedy capture of Leningrad , a major center of military production , in the north . 
