With the introduction of unrestricted submarine warfare in 1916 the Ministry of Munitions became concerned about the availability of foreign iron ore. Baird's were one company amongst others which opened up domestic mines in order to supply the war effort. In May 1916 Baird's signed an agreement to run the mine on behalf of the Ministry, although there was a minor skirmish over the amount of processing to be done on the island. The first prisoners were on the island by June and were housed in the upper part of the village, numbers 17–32 and the now completed 49–64. This northern part of the village was converted into a prisoner-of-war camp by the simple expedient of building a barbed wire fence around it and erecting sentry boxes and arc lamps at the corners.