Political map of Sub-Saharan Africa 7 May 1942 (Operation Ironclad): In December 1941 Japan entered World War II by attacking US and British bases in the Pacific. The following March the Japanese mounted a raid into the Indian Ocean, threatening British holdings there. Concerned that Japan's next move would be to establish itself in Vichy Madagascar, the British landed forces at Diégo Suarez in the north of that island in May (Operation Ironclad).