To modernize the Feste the Germans constructed in 1887 an armored battery for two 21 cm mortars between the two forts. They were the first of a serie of turrets designed by Schumann. These turrets had no recoil system. Instead the glacis plates around the turret and the building had to absorb the entire recoil. The Germans were satisfied with this system, but the 21 cm turrets were considered to be too expensive. At the same time the mortars were not very effective because their rate of fire was too low and the range too short.