At the port of Étaples, the German army built a gun battery with four 170 mm. guns. These modern guns were manufactured by Krupp and had a range of 29 km.
The gun battery was located on the northern side of the mouth of the River Canche River at its entry into the English Channel. A bunker (R688) was built for each gun, with ammunition trays behind the gun room.
Today the four big bunkers are well hidden in the woods.