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.

Chronology

1940

The Regia Marina Red Sea Flotilla based at Massawa provided a focal point for Indian Ocean naval activity following Italian declaration of war on 10 June 1940; although Indian Ocean patrols of Kriegsmarine merchant raiders required defensive dispersion of Allied cruisers after May.

1941

Early focus was Allied neutralisation and capture of Regia Marina African naval bases, followed by invasions of Iraq in April and Iran in August, to displace governments friendly to the Axis powers. Later Allied focus was on destruction of Kriegsmarine commerce raiders and moving troops to defend against anticipated Japanese expansion into south-east Asia.

1942

Japanese submarine cruisers began patrolling the Indian Ocean during the Dutch East Indies campaign. Following the attack on Pearl Harbor, the Kido Butai fast carrier task force raided Darwin, Australia to cover the invasion of Timor and raided Ceylon to cover transport of Japanese troops to Rangoon. Kriegsmarine merchant raiders were less able to avoid Allied patrols; but the battle of the Atlantic spilled over into the Indian Ocean around Cape Agulhas as German Type IX submarines began patrolling the east coast of Africa.

1943

Axis submarine patrols of Indian Ocean trade routes were expanded with establishment of a Kriegsmarine base in Penang as Allied anti-submarine patrols became increasingly effective in the Atlantic. Allied submarines and aircraft began patrolling the Strait of Malacca and Andaman Sea to intercept shipping supporting Japanese forces in Burma.

1944

Use of Ultra intelligence information increased successful interceptions by Allied submarines and reduced Axis resupply opportunities in the Indian Ocean. Surrender of the Regia Marina and destruction of Kriegsmarine battleships made Royal Navy aircraft carriers available for raids of the Andaman Sea.

1945

Allied focus was on amphibious operations along the Burma coast of the Andaman Sea. Axis submarine operations were restricted by fuel shortage and maintenance difficulties.

List of sub-theatres and actions

Sources