This was the Alpine fortress planned by Reichsführer-SS Heinrich Himmler as a national redoubt into which Germany’s government and armed forces could retreat from southern Bavaria across western Austria to northern Italy (November/December 1943).
The plan was never fully endorsed by Adolf Hitler and no serious attempt was ever made to put the plan into operation.
In the six months following the Allied 'Overlord' landings in Normandy on 6 June 1944, the US, British, Canadian and French armies advanced from the west through France and the Low Countries to the Rhine river and appeared fully poised to strike into the heart of Germany, while the Soviet forces, advancing from the east through Poland, reached the Oder river. It seemed likely that Berlin would soon fall and that Germany would be cut in half. In these circumstances, it occurred to both some leading figures in the German régime and to the Allies that it wold be logical for the Germans to move their government to the mountain areas of southern Germany and Austria, where a relatively small number of determined troops could survive for an extended period.
A number of intelligence reports to SHAEF (Supreme Headquarters of the Allied Expeditionary Forces) indicated that this area held stores of foodstuffs and military supplies built up over the preceding six months, and could even be harbouring armament production facilities. Within this fortified terrain, these intelligence reports suggested, Hitler would be able to evade the Allies and cause tremendous difficulties for the occupying Allied forces throughout Germany.
The German minister of propaganda, Dr Joseph Goebbels, established a special unit to invent and spread rumours about such an 'Alpenfestung'. Goebbels also organised the dissemination to neutral governments of rumours to this effect, thus keeping alive the myth of a German national redoubt but carefully omitting any hint of its state of readiness. Goebbels enlisted the assistance of the Sicherheitsdienst, the intelligence branch of the SS, to produce false blueprints and reports on construction supplies, armament production and troop transfers to the redoubt. This successful deception of Allied military intelligence is considered to be one of the greatest successes of the German intelligence apparatus during the entire war, but was altogether too late to exercise any real effect on the course of the war’s closing stages.
Although he never endorsed the plan, on 24 April 1945 Hitler issued an order for the evacuation of remaining government personnel from Berlin to the redoubt; he made it clear that he himself had no intention of leaving Berlin, even if it fell to the Soviets, as it did on 2 May. When the US armies penetrated into Bavaria and western Austria at the end of April, they met little serious resistance, and the national redoubt was shown to have been a myth. Even so, this myth entailed major military and political consequences. Once the armies of the Western Allies had crossed the Rhine river and advanced into western Germany, they had to decide whether to advance on a narrow front towards Berlin, or on a broad front with a view to securing both the North Sea coast and southern Germany before advancing farther to the east. Lieutenant General George S. Patton, the commander of the US 3rd Army, had consistently advocated a narrow-front advanced ever since D-Day, and did so again at this point. The Allied commander-in-chief, the American General Dwight D. Eisenhower, took a more cautious view, and it was his broad-front strategy which prevailed.
The 'Alpenfestung' was one of three reasons associated with SHAEF’s movement of some Allied forces toward southern Germany rather than towards Berlin which, it had been agreed, was to be in the Soviet zone of occupation, and the battle for which would have entailed unacceptably high Western Allied casualties.
In February 1945, the SS evacuated V-2 rocket scientists from the Peenemünde army research centre to the 'Alpenfestung'. In February and early in March of the same year, SHAEF received reports that German military, government and Nazi party departments and their staffs were leaving Berlin for the area around Berchtesgaden, the site of Hitler’s retreat in the Bavarian Alps. SS-Obergruppenführer und General der Waffen-SS Gottlob Berger later claimed that Hitler had signed an order on 22 April to evacuate 35,000 prisoners to the 'Alpenfestung' as hostages, but that he had not carried out the order. It is worth noting along similar lines that many industrial facilities, such as Mittelwerk, which had been evacuated to remote locations, also failed to obey Hitler’s order requiring that they be demolished rather than yielded to the advances from west and east.