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There was a degree of paranoia involved in the planning and construction of the Maginot Forts. In 1916, Fort Douaumont was captured from its garrison with the minimum of force when the Germans approached the fortress and on receiving no challenge, pressed forward, entering the fort via an unguarded open window. Douaumont's garrison consisted of what were considered infirm troops (essentially older elderly troops who were at the very limits of their serviceable usefulness) and the fall of the largest fortress defending Verdun in such humiliating circumstances would go on to form a distrust of older reservist troops by the French military command. This had two main ongoing influences to the Line's planners: 1) Older troops were never going to be used again in fixed defence structures. 2) Every potential access point to a fortification would be provided with means of strong defence (relative to the perceived potential risk).

The concept of a defensive firing chamber was itself nothing new. At its most basic, such provisions can be seen in castles of the Medieval era; by the advent of the more modern fortifications these had evolved into more complex solutions. The musket galleries were soon augmented with the addition of caponiers, described as bomb-proof structures designed to provide suppressing fire against attackers. All entrances to a Maginot Fort were not as they would initially appear; no door led directly into a building, as the visible door merely formed an outer barrier, behind which was located a machine gun, with the actual entrance off to one side out of view from the exterior. Additionally, smalls arms fire from a machine gun was used to prevent a would-be attacker from even getting this close!

Due to the complex nature of a firing chamber designed to mount twin MAC 31 machine guns, we opted to re-create the simpler version where a single FM 24/29 was deployed. This decision was also based on obtaining the components for the latter (see below).