 The improvements addressed the shortcomings revealed by the Battle of Liège, allowing the fortress ring to be a backstop to the primary line of fortifications farther east.The Liège ring was designated PFL II, although the forts on the west side of the river were part of PFL IV.Improvements included replacing 21 cm howitzers with longer-range 15 cm guns, 150mm howitzers with 120mm guns, and adding machine guns.