In 1915 he moved to Switzerland to take advantage of Swiss neutrality. Arp later told the story of how, when he was notified to report to the German consulate in Zurich, he pretended to be mentally ill in order to avoid being drafted into the German Army: after crossing himself whenever he saw a portrait of Paul von Hindenburg, Arp was given paperwork on which he was told to write his date of birth on the first blank line. Accordingly, he wrote "16/9/87"; he then wrote "16/9/87" on every other line as well, then drew one final line beneath them and, "without worrying too much about accuracy", calculated their sum. Hans Richter, describing this story, noted that "they German authorities believed him."