On 16 January, Hitler returned to the partly bombed Chancellery in Berlin to be nearer to the Eastern Front. He now decided that the Western Front should go on the defensive to release troops to fight in the east. He also decided that they must hit the southern flank of the Russian spearhead and Hitler ordered Guderian to send the Sixth Panzer Army to Hungary. It was necessary, Hitler said, to hang on to the oil fields in Hungary, otherwise there would be no fuel for the Panzers.
General Nehring's XXIV Panzer Corps was stemming the Russian attack around Kielce, but the XLVI Panzer Corps had to pull out of the Warsaw area when it risked being encircled. It was supposed to go south to stop a Russian breakthrough that would cut East and West Prussia off from the rest of Germany. But the Russians threw it back on to the north bank of the Vistula and began their dash on the German border unhindered.
The German garrison in Warsaw now risked being cut off. Guderian told Hitler that they should be withdrawn, but he grew angry and insisted that Warsaw be held at all costs. But the garrison commandant had little artillery and only four infantry battalions with limited combat experience. It would have been impossible for them to hold the city and the commandant withdrew his garrison despite Hitler's orders not to. Hitler was furious and spent the next few days investigating the loss of Warsaw rather than devoting himself to more pressing matters. When Hitler ordered the arrest of members of the general staff, Guderian said that he alone was responsible for the loss of Warsaw, so it was he who should be arrested, not his staff. Nevertheless Hitler had three of Guderian's staff arrested at gunpoint. Guderian again insisted that he was the one whose conduct should be investigated, so ending up subjected to lengthy interrogations at a time when he should have been concentrating all his efforts on the battle for the Eastern Front. Two of his staff were then released, but instead of returning to their staff duties were sent to command regiments on the Eastern Front. Three days later one of them was killed. The third member of Guderian's staff was sent to a concentration camp, which he later swapped for an American prisoner of war camp.
On 18 January, the Germans in Hungary attacked in an attempt to lift the siege of Budapest. They fought their way through to the banks of the Danube. But that same day the Russians entered the city, so the effort had been wasted. Nevertheless Hitler sent the Sixth Panzer Army to Hungary in an attempt to hold the Russians there.
On 20 January, the Russians first set foot on German soil. Guderian's wife, who had been under constant surveillance by the local Nazi Party, was then allowed to leave and flee to the safety of Guderian's headquarters, half an hour before the first shell landed in Deipenhof.
The Russian onslaught could not be resisted. Hitler began to accuse his Panzer commanders of treason. Guderian tried to calm him, but Reinhardt and Hossbach were relieved of their commands.
The Russians had now mastered the art of Panzer warfare. They advanced rapidly, bypassing strongpoints and outflanking fortified lines - though most of the fortifications in the east had been stripped to build the Atlantic Wall. Germany's only hope now was that the Western Allies would realize what the rapid Russian advance might mean for the future of Europe and sign an armistice. Guderian said that he proposed to the German foreign minister von Ribbentrop that he open negotiations for an armistice on at least one front - preferably the Western. Von Ribbentrop told Guderian that he was a loyal follower of Hitler and he knew that the Führer did not want to make peace.
`How would you feel if in three or four weeks the Russians were at the gates of Berlin?' said Guderian.
`Do you believe that that is possible?' asked a shocked von Ribbentrop.
When Hitler heard of this, Guderian too was accused of treason, though he was not arrested. Hitler had few enough able officers left.
Guderian proposed a plan that would give them some breathing space. They should form a new army group specifically to hold the centre of the line. Guderian suggested that its commanding officer should be Field Marshal Freiherr von Weichs, a commander in the Balkans. Hitler approved Guderian's plan for the creation of a new army group, but gave its command to Himmler. Guderian was appalled. Himmler was not a military man. He was a politician, the head of the SS. He was also chief of police, minister of the interior and Commander in Chief of the Training Army, any one of which positions might be thought a full-time job. But Hitler was insistent. Guderian tried to persuade him at least to give Himmler von Weichs' experienced staff. But Hitler, who was now wary of all his generals, ordered Himmler to choose his own staff. Himmler surrounded himself with other SS leaders who were largely, in Guderian's opinion, incapable of doing the jobs they had been given. SS Brigadenführer Lammerding was his chief of staff. Previously the commander of a Panzer division, Lammerding had no idea of the duties of a staff officer. The new army group was to be called Army Group Vistula, though the Russians had crossed the Vistula months before.
Hitler set up new `tank destroyer' divisions. These consisted of men issued with antitank grenades and bicycles. Somehow they were expected to stop the huge armies of T-34s that were now driving westwards. And by this time 16-year-old boys were being conscripted into the army.
By 28 January, Upper Silesia was in Russian hands. Speer wrote to Hitler saying, `The war is lost.' Hitler now cut Speer completely and refused to see anyone alone in private, because they always told him something he did not want to hear. Hitler began demoting officers on a whim, and brave soldiers denounced by party members found themselves in concentration camps without even the most summary investigation. Guderian found that more and more of his day was spent listening to lengthy monologues by Hitler as he tried to find someone to blame for the deteriorating military situation. Hitler often became so enraged that the veins on his forehead stood out, his eyes bulged and members of staff feared that he might have a heart attack.
On 30 January, the Russians attacked the Second Panzer Army in Hungary and broke through. Guderian proposed evacuating the Balkans, Norway and what remained of Prussia and bringing back all the Panzers into Germany for one last battle. Instead Hitler ordered an attack and on 15 February the Third Panzer Army under General Rauss went on the offensive. In overall command of the offensive was General Wenck. But on the night of the 17th, after a long briefing by Hitler, Wenck noticed that his driver was tired and took the wheel, only to then fall asleep himself and crash into the parapet of a bridge on the Berlin-Stettin highway. Wenck was badly injured and, with him in hospital, the offensive bogged down and never regained its momentum.
In March, Rauss was summoned to the Chancellery and asked to explain himself. Hitler did not give him a chance to speak. After he had dismissed Rauss, Hitler insisted he be relieved of his command. Guderian protested that he was one of the most able Panzer commanders. Hitler said that he could not be trusted because he was a Berliner or an East Prussian. It was then pointed out that Rauss was an Austrian, like Hitler himself. Even so he was relieved of his post and replaced by von Manteuffel.
Himmler's Army Group Vistula did little to halt the Russian advance and Guderian eventually suggested that Himmler be replaced. On 20 March, Hitler agreed. He was replaced by a veteran military man, Colonel-General Gotthard Heinrici, who was currently commanding the First Panzer Army in the Carpathians. Under his command was the Third Panzer Army under von Manteuffel.
Guderian continued to come up with suggestions of how the Russian advance could at least be slowed. But after one final falling-out with Hitler, he was ordered to take convalescent leave of six weeks. He left Berlin on 28 March intending to go to a hunting lodge near Oberhof in the Thuringian Mountains, but the rapid advance of the Americans made this impossible. Instead he decided to go to the Ehenhausen sanatorium near Munich for treatment of his heart condition. Warned that he might invite the attentions of the Gestapo, Guderian arranged to be guarded by two members of the Field Police.