Interval casemates were all based on a series of standard plans.
However, these could be modified/altered by the STG to meet local situations like the terrain
features or the role of the casemate (e.g. observation).
In general one can say that (the ones designed by CORF) they were two-storey (ground floor and basement) reinforced concrete structures about 15 to 20m in width.
Exceptions can be found along the Rhine, were it was not possible to build a two storey casemate so close to the water.
The same goes for casemates in heavily forested areas (woods of Mormal and Raismes)
The distance between interval casemates was decided at 1200m. However, when budget cuts were unavoidable, this distance was often stretched to 2000m or even further, thereby endangering the casemates’ ability to cover the top of flanking fortifications because of a limitation of the max. range of at least the FM machine guns.
Either a single casemate, that had positions for weapons on one flank (1 firing chamber), or a double casemate that had weapons on two flanks (2 firing chambers).
Sometimes, the terrain situation made it not possible to build a double casemate. In these cases, a pair of ‘casemates simples’ were build, positioned back-to-back so that they fired in opposite directions. Often, a subterranean passage connected them.
A ‘coupole GFM (guet fusil-mitrailleur)’ can be found on the rooftop for observation and close-in defence.
An example of a first generation structure is CORF casemate de la Route-d'Outange Est (SF Crusnes).
Came into being after introduction of the JM cupola (1931).
Sometimes, these cupolas replaced a concrete embrasure, thus reducing the frontal surface (e.g. casemate Praucourt, SF Crusnes).
A JM cloche was also a more difficult target to hit and it enabled designers to sometimes reduce the number of embrasures, or increase the ability for frontal fire.
Sometimes all the armament was mounted in cupolas (casemate cuirassée). There were two or three cloches (a GFM and two JM’s). This specific type had no moat and two entrance doors. An embrasure for a ‘fusil-mitrailleur’ protecting these with flanking fire was not standard.
They were not numerous. Six for example were build in the Fortified Sector (in French: SF) of Crusnes and two in the SF of Thionville to name just a few.
An example of a second generation structure is CORF casemate Quatre Vent Nord.
The third generation of CORF interval casemates came into being during the ‘New front’ building phase.
These casemates can be recognised by the following characteristics:
An example of a third generation structure is CORF casemate Thonne-le-Til.