These shelters were mainly constructed by forced labor from the Arbeitslager Reichenau in Innsbruck. 25 underground shelters with a total length of 11.2 km and space for 28,755 civilians were built in 1944.
During the next six months attacks were suspended by the Allies because of preparations for Operation Overlord in Normandy, in France. In this break the military and urban administration of Innsbruck rearranged the anti-aircraft defenses and expanded the air raid shelters.