Judging by the helmets on the troops and the body of water behind them, that's a German Atlantic Wall pillbox using an obsolete PzKpfw II turret (or PzKpfw I ausf C, which used a similar turret) after the fortifications have been overrun by American troops, which would make it either Utah or Omaha beach.
The Germans did a number of conversions like this, using obsolete French and German tank turrets. IIRC, for the defense of Berlin and in Italy, they were using front-line tank turrets, like the Pzkpfw V 'Panther', for pillboxes, as well.
