During the Second World War, 1939–1945, Fuller was under suspicion for his Nazi sympathies. He continued to speak out in favour of a peaceful settlement with Germany. Alan Brooke (in his war diaries, p. 201) comments that "the Director of Security called on him to discuss Boney Fuller and his Nazi activities", but Brooke commented that he did not think Fuller "had any unpatriotic intentions". Although he was not interned or arrested, he was the only officer of his rank not invited to return to service during the war. There was some suspicion that he was not incarcerated in May 1940 along with other leading officials of the BUF because of his association with General Edmund Ironside and other senior officers. Mosley himself admitted to "a little puzzlement" as to why Fuller had not been imprisoned.