In June 1940, the Channel Islands - British Crown Dependencies - were occupied by German forces. On the orders of Adolf Hitler, they were transformed into impregnable fortresses, works that still mark the islands today. Measuring just three square miles, the island of Alderney now found itself one of the most heavily fortified places in the world. But the island's wartime story didn't end there. The majority of the island's population were evacuated to the mainland prior to the occupation but a small number chose to return to their homes despite the trials of living alongside the enemy. The two communities weren't alone, they were joined by thousands of foreign labourers - slave labour - who endured meagre rations and rampant disease. To house the influx of POWs, the German occupiers built four camps on Alderney, including Lager Sylt - the only concentration camp on British soil.