of 120 millimetres, an overall height of 1.6 metres of which only 0.65 metres protruded above the bunker. There was another machine gun in a flank fire position of the bunker that covered the entrance. It is not entirely clear which machine gun was used here. The weapon was fixed to a box stand (Untersetzkasten) with the corresponding gun mount. The flank fire position had a 7P7 armoured embrasure plate with a thickness of 10 centimetres and a weight of 7.5 tonnes, in front of which there was a stepped embrasure made of concrete. By means of a slide, the embrasure and observation slit could be closed. In addition, for the viewing slit there was a sliding plate of armoured glass which could be used to observe the situation when under fire. Technical facilities Power The engine room took up two floors, the upper floor could only be entered through the engine room from below. The bottom of the upper floor consisted of steel beams and plates. For power generation, the bunker had two diesel generators in the engine room. These were water-cooled, four-cylinder, four-stroke engines, generating 38 hp each. The alternators each produced 28 kW of three-phase, alternating current at 380 volts. This powered the electric motors in the bunker, the electric heaters in the accommodation and the boilers and hobs in the kitchen. The main lighting was supplied at 220 volts. Sensitive areas were operated by accumulator batteries to ensure continuity of power available in case the generators failed. This delivered a 24 volt power supply to light the battle positions and the optics as well powering the emergency lighting. The radio room of the bunker had its own separate 24-volt batteries. Today, the generators have been removed. Air filter system and ventilation An important aspect of the bunkers of the Siegfried Line was their ability to operate under gas attack. The bunkers could be hermetically sealed and supplied with purified air from outside. Because of their importance, the B-Werke had the most elaborate filter systems designed and built into the facilities. A constant overpressure prevented the penetration of gases in the event of minor leaks and allowed the removal of stale air and exhaust gases from the battle positions. One or more spaces were combined to form gas-tight cells. Pressure relief valves in the rooms or cells regulated the pressure. The air sucked in from outside was