Given its location overlooking the Baie d'Authie and English Channel it's no wonder a large gun batterie was planned here.
The plans included an incredible seven big casemates and four heavy machine gun bunkers, although not all were constructed in time before the Allies captured the area.
Like many batterie sites, this area started with quickly-built but unprotected open emplacements for field cannons which were later replaced by the larger casemates.
Perched high on the dunes near to the sailing club at the north of the town, only two of the planned four R671 casemates were built with a third under construction but never completed. If you're careful negotiating the high dunes they can be visited but be aware they have also been used to dump rubbish inside and there is a lot of broken glass. The higher of the two casemates has also received a number of heavy blows to the rear entrance and gun room which could have come from detonating explosives inside the casemate as the damage is too great for tank or artillery rounds.
Both R671 casemates feature unique patterns in the outer concrete to help break up the sharp outline of the curved buildings and encourage vegetation growth for camouflage.
An R636 batterie command post with observation and communications facilities - similar to that of nearby Stp Quend Plage - was also started but never finished.
Some of the completed builds, including a R612 casemate, a R640, and several machine gun positions were removed post war as the town recovered from the occupation.
Inland of the beach side casemates you can find Batterie Fort Mahon Plage Nord Est where there were originally six open emplacements for 105mm field guns plus a large area of accommodation buildings including eight double Wellblech shelters and ten smaller personnel shelters. Today only one can easily be seen - along the Rue de Jardin - with the rest buried nearby or covered over by housing.