Abri de Kronprinz - Argonne. HQ bunker of German Crown Prince Wilhelm in the Argonne The Argonne Massif is a narrow 12km wide band of hills rising steeply to the west of the Meuse valley. For four years of bitter fighting the front line ran east-west across these hills until the American offensive here in the autumn of 1918 which was a major test for the American army for many of whose troops this was their first real experience of battle.