Japan's entry into the war in 1941 led to the capture of European South-east Asian colonies such as British Malaya and the Dutch East Indies. In May and June 1942, Japanese submarines began operating in the Indian Ocean and had engaged British forces in Madagascar. The British had invaded the Vichy-controlled island in order to prevent it from falling into Japanese hands – however, as Japan was never known (from post-war evaluation) to have had plans to place Madagascar within its own sphere of influence, Britain's defense of the island could also have been surmised to have been a plausible defense against any possibility of Madagascar falling under Germany's own ambitions.