During the final months before liberation, the camp's commander Franz Ziereis prepared for its defence against a possible Soviet offensive. The remaining prisoners were rushed to build a line of granite anti-tank obstacles to the east of Mauthausen. The inmates unable to cope with the hard labour and malnutrition were exterminated in large numbers to free space for newly arrived evacuation transports from other camps, including most of the subcamps of Mauthausen located in eastern Austria. In the final months of the war, the main source of dietary energy, the parcels of food sent through the International Red Cross, stopped and food rations became catastrophically low. The prisoners transferred to the "Hospital Subcamp" received one piece of bread per 20 inmates and roughly half a litre of weed soup a day. This made some of the prisoners, previously engaged in various types of resistance activity, begin to prepare plans to defend the camp in case of an SS attempt to exterminate all the remaining inmates.