Realizing this, the Germans had not risked an attack, but after long study of the defences had decided that by means of artillery they might shell the Belgians, who held the dunes, and destroy them as they lay in the hollows. So a heavy battery had been planted along the German lines for this work, while in defence the Belgians confronted them with their own famous dog artillery, consisting of the deadly machine guns. The battle of December twentieth therefore began with an artillery duel, resulting in so many casualties that the Red Cross workers found themselves fully occupied.