In May 1939, Harrer was selected by the German Himalayan Foundation to take part in a new expedition to the Nanga Parbat, under the leadership of Peter Aufschnaiter. Their goal was to scout new ways to ascend the north-western face. They explored the Diamir Face with the aim of finding an easier route. They concluded that the face was a viable route, but the Second World War intervened and the four men were interned by the British in Dehradun, India. Harrer's escape and subsequent wanderings across the Tibetan Plateau became the subject of his book Seven Years in Tibet. Some evidence of this expedition is kept in the National Archives of Washington, D.C.