This work anayzes events surrounding the Yokohama incident (1942–1945), which led to the arrest of dozens of journalists and researchers in Japan during the Pacific War period. Utilizing government documents, legal records, postwar memoirs, and information obtained during personal interviews, the discussion concentrates on changes in the treatment of the suspected dissidents in Japan from the 1930s to 1945, and the problems within the system of internal security and thought control during the Pacific War. Attention is also focused on the legal campaigns of some of the Japanese victims of the wartime state from 1945 to the present.