 The German defensive preparations and the lack of any defense in depth indicated that their plan was to stop the invasion at the beaches . Four lines of obstacles were constructed in the intertidal zone . The first , a non @-@ contiguous line with a small gap in the middle of Dog White and a larger gap across the whole of Easy Red , was 250 m ( 270 yd ) out from the highwater line and consisted of 200 Belgian Gates with mines lashed to the uprights . 30 meters ( 33 yd ) behind these was a continuous line of logs driven into the sand pointing seaward , every third one capped with an anti @-@ tank mine . This defensive measure was not as effective as the Germans would have wished . Another 30 meters ( 33 yd ) shoreward of this line was a continuous line of 450 ramps sloping towards the shore , also with mines attached and designed to force flat @-@ bottomed landing craft to ride up and either flip or detonate the mine . The final line of obstacles was a continuous line of hedgehogs 150 meters ( 160 yd ) from the shoreline . The area between the shingle bank and the bluffs was both wired and mined , and mines were also scattered on the bluff slopes . To some extent , the German barricades set up to prevent tanks advancing on the shores became useful to Allied infantry as they provided cover from machine gun and small arms fire . 
