In the mid-1920s the French high command appointed a new set of commissions to study the future defences of the French border in the north as well as in the Alps: the Commission de défense du territoire (CDT), Commission de défense de la frontière (CDF) and Commission d’Organisation des Régions Fortifiées (CORF). The mixed-arms turret was a refurbished M1905 75mm gun turret left over from World War I.
The 135mm and 81mm housed curved fire mortars. The turrets ranged from 1.98m in diameter for the machine-gun turret to 4m for the 75mm M1933 turret for two guns.
There were six types of turrets used in the Maginot Line, in different sizes and styles.
