The French anticipated that the enemy, read the Germans, would start their attack on the Maginot Line with an heavy bombardment followed by an infantry attack. In that case the infantry would use the shell holes for cover. Then the machine guns in the turrets would be useless. Therefore most of the machine gun turrets were equipped with a 50 mm mortar. This weapon was unusual in having a fixed elevation. The range was changed by turning a valve near the breech of the weapon. The version shown was installed in a turret and had an elevation of 20°. The casemate mounting had an elevation of 45°. The weapon was considered to be very succesful. Large numbers were used by the Germans in their Atlantikwall. For more information click here.