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