passed through a pre-filter, which cleared the air of dust and water vapour. Then it flowed through four, parallel, room filters, which filtered dangerous gasses out using active carbon inserts. If required, the air for heating the bunker could be warmed using a heat exchanger before being blown into the bunker. The capacity of the central fan was 40 m³ / minute. To ensure the ventilation of the plant even in the event of the central fan failing, individual rooms or cells had hand-operated HES ventilators (army unit protection ventilators) with 1.2 m³ or 2.4 m³ capacity per minute. The central fan and its filters was located above the engine room but is no longer in place. Communication facilities The bunker had a sophisticated array of communication facilities. Three underground cables of the fortress telephone network were terminated in a separate radio room, where there was a switchboard. Its inputs included slots into which field cable could also be connected either to provide additional cable connections or to bridge damaged underground cable. Telephones were installed in the most important room or at least connections for portable telephones were available. The turrets were connected independently of the central exchange in the radio to the associated battle preparation rooms with separate telephone lines. Voicepipes were used to link the inner entrance defence rooms and the flank fire position. Water supply The bunker had its own well. In the well chamber was a pump that pumped the water into a tank. From there water was pumped into a pressure vessel in order to provide the necessary water pressure to the taps. There were take-off points in the kitchen, the sick bay, the command post, the hallways and the washroom. The bunker only had wash basins, there were no showers, in the toilets and in the engine room. In addition to the need for drinking water, water was needed to cool the diesel generator sets and there was also an automatic sprinkler system in the ammunition store. Waste water was collected in a pit from where it was pumped to the surface by an electric pumping system activated by a float. Manning during the Second World War The Besseringen B-Werk was first used in the period after its completion until summer 1940, when its occupation no longer seemed necessary following the successful German invasion of France. In autumn 1944 it was manned again. After