After his doctorate, Arrupe was sent to work as a missionary in Japan. His early years as missionary were very frustrating for him. No matter what he did, what he organised, people did not attend, and few if any converted to Christianity. When the attack on Pearl Harbor occurred in Hawaii on 7 December 1941, it was 8 December in Japan. Arrupe was celebrating the Eucharist for the Solemnity of the Immaculate Conception when he was arrested and imprisoned for a time, being suspected of espionage. On Christmas Eve, Arrupe heard people gathering outside his cell door and presumed that the time for him to be executed had arrived. However, to his utter surprise, he discovered that some fellow Catholics, ignoring all danger, had come to sing him Christmas carols. Upon this realization, Arrupe recalled that he burst into tears. His attitude of profound prayer and his lack of offensive behaviour gained him the respect of his jailers and judges, and he was set free within a month.