Al Murray and James Holland head to Arromanches where following D-Day, the British built the Mulberry B harbour -- a concrete megastructure constructed in pieces in the UK and then, incredibly, floated across the English Channel and anchored in Normandy to deliver 550,000 tons of allied supplies. The remnants of Mulbery Harbour are visible today. Al and James take in the sheer scale of this military engineering and logistics endeavour on a steep walk from the beach to the top of the cliff and pause to overlook and reflect on this magnificent reminder of the  allied efforts involved in Operation Overlord.