Generals 'December and January' to the rescue

The Germans got as close as 60 kilometres to Moscow, but a Russian counter attack in December 1941 meant that they would advance no further. Despite capturing a staggering 3 million Russian prisoners by the end of 1941, the Germans had not captured either Leningrad or Moscow as planned. It was now that the significance of the delay in the launch of Barbarossa (because of the attack on Yugoslavia) became clear. Hitler had expected his campaign in Russia to be over before the Russian winter set in, but it was not. His troops were not ready for a winter war. Most had no winter clothing and thousands suffered from frost-bite. Oil froze in the engines of tanks and trucks. The Russians, on the other hand, were well prepared for the weather.

Equally disastrous for the Germans was their underestimation of the size of the Russian army. They thought the Russians had 200 divisions (about 3 million men), but instead, they had 360 divisions (5.4 million men). No matter how many Russian armies the Germans destroyed or captured, there always seemed to be more to replace them.

Probably the most important factor of all was that Hitler had confidently expected to capture or at least destroy most of Russia's industries. This is because most of Russia's factories were located in the west of the country and this was quickly under German occupation. But Stalin had ordered 1500 factories to be moved as soon as the invasion took place. Ninety per cent of these were involved in weapons production, and they were now operating far from the reach of the Germans.

Neil Demarco: The era of the Second World War; Oxford University Press; 1993/2000, page 39