Indian Ocean in World War II

Prior to World War II, the Indian Ocean was an important maritime trade route between European nations and their colonial territories in East Africa, the Arabian Peninsula, British India, Indochina, the East Indies (Indonesia), and Australia for a long time. Naval presence was dominated by the Royal Navy Eastern Fleet and the Royal Australian Navy as World War II began, with a major portion of the Royal Netherlands Navy operating in the Dutch East Indies and the Red Sea Flotilla of the Italian Regia Marina operating from Massawa.

Axis naval forces gave a high priority to disrupting Allied trade in the Indian Ocean. Initial anti-shipping measures of unrestricted submarine warfare and covert raiding ships expanded to include airstrikes by aircraft carriers and raids by cruisers of the Imperial Japanese Navy. A Kriegsmarine Monsun Gruppe of U-boats operated from the eastern Indian Ocean after the Persian Corridor became an important military supply route to the Soviet Union.