Some of the techniques used by the inmates were ingenious and not too dissimilar to those shown in the (postwar) war film "The Great Escape" about Allied POWs. Excavating the tunnels was not easy because of the heavy clay soil upon which the camp was built. Cans, meat tins, and even knives from the canteen were used as digging implements. The soil was hauled out of the tunnel on a makeshift skip and put into kit bags. At first, prisoners carried the soil in their pockets to the long-jump pit or garden plots. Others kneaded clay into balls and dropped them through a hole in a false wall they had constructed in an unused room in one of the huts. To support the tunnel roof, oak benches were stolen from the canteen and bed legs were cut down when supplies of wood were depleted. A ventilation pipeline was made from condensed milk tins; air was forced through by a hand-operated fan. The tunnel even had its own electric lights, tapped off the mains supply. Noise was concealed by chorus singing.