It could take as little as three minutes from the time the enemy was spotted by the observers until they were fired upon. There were three types of observations posts. Each block, or casemate, had two observation domes, one the surveillance position, manned by an officer equipped with binoculars with which to constantly scan the ground. The dome on the opposite end of the block was manned by an NCO, whose mission was to register any targets spotted by the officer. The NCO used a powerful 21cm periscope in the roof of the turret. Closer to the frontier were auxiliary observation posts manned by one person with a periscope. The third type of observation post was located at the entrance of the block or casemate and protected the casemate itself from attacking infantry. Each observation dome had three openings, called embrasures, which held periscopes, automatic rifles, or 50mm mortars. Each observation dome was reached by a ladder and the floor could be raised or lowered to suit the height of the observer. They were connected by telephone to the artillery or infantry command post.
In case of attack, the officer would identify the target and, using a panoramic photograph, notify the command post of its bearing and elevation. The NCO, listening through an acoustic tube would pinpoint the exact coordinates and pass this on to the command post. A telephone operator would receive the message and write the information on a blackboard. The command post staff passed on the information to the artillery commander, who decided whether or not to fire, and if so, which block would be detailed to fire. Information was then relayed to the chosen block's commander, who was in the same room as the artillery commander.
The block commander gave the order for the number of rounds, type of shell, and fusing. This was passed to the gunlayer by means of a pointing mechanism revolving around a dial, like on a ship's bridge. When the "ALERT" signal was given, the gun crew would go to their positions, the airlock door leading from the main gallery to the base of the combat block was closed (each block had its own airlock system, consisting of two sets of doors), the interior air pressure mounted to keep fumes from reaching the galleries, and the turret was raised into the firing position. Shells were taken from the racks in the lower level of the turret, placed into the hoists, and lifted to the firing chamber. There, four men, two layers, and two loaders, cramped under the cupola roof, manned the guns. The turret was turned to face the target and the gun elevated. The shells were placed in the breeches, the gun was fired, the breeches were opened, and shells ejected. Once finished, the observers reported the results.
Gun crews were on a three-watch system - duty, stand-by, and rest. Combat personnel were kept in the first two statuses. Those on stand-by joined those on duty when the alert sounded. The garrison found that it was best to stay at the blocks rather than trudge sometimes long distances back to the barracks, although the barracks were the only place to get uninterrupted sleep during the constant firing. The officers had no relief as they were on duty day and night.
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