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.
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
15 November 1939: Australian, British and French warships began patrolling the Indian Ocean when the German pocket battleship Admiral Graf Spee sank the tanker Africa Shell south of Madagascar.
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.
23 March 1940: The Royal Navy established the Malaya Force of cruisers, destroyers and submarines to stop German merchant ships leaving the Dutch East Indies.
11 May 1940: German merchant raider Atlantis entered the Indian Ocean from the South Atlantic.
7 June 1940: Italian warships began minelaying off Massawa and Assab.
10 June 1940: Eight Italian submarines began war patrols of the Indian Ocean from Massawa. Some of these submarines were lost because leakage of chloromethane air conditioning refrigerants caused central nervous system poisoning of their crews from recirculating air during submerged operations.
10 June 1940: Atlantis captured the freighter Tirranna in the Central Indian Ocean.
16 June 1940: Italian submarine Galileo Galilei sank the tanker James Stove.
19 June 1940: Galileo Galilei was captured by the British naval trawler Moonstone.
23 June 1940: Italian submarine Torricelli sank HMS Khartoum before being sunk by accompanying destroyers.
24 June 1940: Italian submarine Galvani sank the sloop HMIS Pathan before being sunk by the sloop HMS Falmouth.
11 July 1940: Atlantis sank the freighter City of Bagdad south of India.
13 July 1940: Atlantis sank the freighter Kemmendine south of India.
2 August 1940: Atlantis sank the freighter Tallyrand in the central Indian Ocean.
17 August 1940: Royal Navy and Royal Australian Navy cruisers and destroyers covered the withdrawal of British troops from British Somaliland to Aden.
24 August 1940: Atlantis sank the freighter King City in the Central Indian Ocean.
26 August 1940: German merchant raider Pinguin sank the tanker Filefjell south of Madagascar.
27 August 1940: Pinguin sank the tanker British Commander and the freighter Morviken south of Madagascar.
6 September 1940: Italian submarine Guglielmotti sank the tanker Atlas in the Red Sea.
9 September 1940: Atlantis sank the tanker Athelking in the central Indian Ocean.
10 September 1940: Atlantis sank the freighter Benarty in the central Indian Ocean.
12 September 1940: Pinguin sank the freighter Benavon east of Madagascar.
16 September 1940: Pinguin captured the freighter Nordvard in the central Indian Ocean.
20 September 1940: Atlantis sank the liner Commissaire Ramel west of Sumatra.
7 October 1940: Pinguin captured the tanker Storstad south of Java.
21 October 1940: Italian destroyer Francesco Nullo was sunk during the battle of Mumbai to Suez Canal convoy BN 7.
22 October 1940: Atlantis captured the freighter Durmitor west of Sumatra.
9 November 1940: Atlantis sank the freighter Teddy west of Sumatra.
10 November 1940: Atlantis captured the tanker Ole Jacob west of Sumatra.
11 November 1940: Atlantis sank the freighter Automedon west of Sumatra.
18 November 1940: HMS Dorsetshire shelled Italian Somaliland.
18 November 1940: Pinguin sank the freighter Nowshera west of Australia.
20 November 1940: Pinguin sank the freighter Maioma west of Australia.
21 November 1940: Pinguin sank the freighter Port Brisbane west of Australia.
30 November 1940: Pinguin sank the freighter Port Wellington in the central Indian Ocean.
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.
24 January 1941: German merchant raider Atlantis sank the freighter Mandasor north of Madagascar.
31 January 1941: Atlantis captured the freighter Speybank north of Madagascar.
2 February 1941: HMS Formidable aircraft raided Mogadishu as Operation Breach. Atlantis captured the tanker Ketty Brövig north of Madagascar.
3 February 1941: German pocket battleship Admiral Scheer entered the Indian Ocean from the South Atlantic.
10 February 1941: HMS Shropshire, Hermes, Hawkins, Capetown, Ceres and Kandahar formed Force T supporting the Allied offensive against Italian Somaliland from Kenya.
13 February 1941: Fourteen Fairey Albacore from HMS Formidable sank SS Monacalieri in the Operation Composition raid on Massawa.
20 February 1941: Admiral Scheer sank the freighter Grigorios C and captured the tanker British Advocate north of Madagascar.
21 February 1941: Seven Fairey Albacore from HMS Formidable raided Massawa. Admiral Scheer sank the freighter Canadian Cruiser north of Madagascar.
22 February 1941: Admiral Scheer sank the freighter Rantaupandjang north of Madagascar.
27 February 1941: Action of 27 February 1941, HMS Leander sank the Italian merchant raider Ramb I west of the Maldives.
1 March 1941: Five Fairey Albacore from HMS Formidable raided Massawa.
3 March 1941: Admiral Scheer returned to the South Atlantic to evade Allied warships.
4 March 1941: The four surviving Italian submarines abandoned the Massawa base and escaped into the South Atlantic. The German supply ship Coburg and prize Ketty Brövig were scuttled when stopped by HMAS Canberra and HMNZS Leander, north of Madagascar.
16 March 1941: Invasion of Berbera by Royal Navy Force D.
23 March 1941: The German SS Oder was scuttled when stopped by HMS Shoreham in the Gulf of Aden.
1 April 1941: The German SS Bertrand Rickmers was scuttled when stopped by HMS Kandahar.
8 April 1941: Six Italian destroyers and 17 Axis merchant ships were sunk or scuttled when Allied troops captured Massawa. Atlantis left the Indian Ocean via the South Atlantic.
19 April 1941: British invasion of Basra prelude to the Anglo-Iraqi War.
25 April 1941: German merchant raider Pinguin sank the freighter Empire Light in the Arabian Sea.
28 April 1941: Pinguin sank the freighter Clan Buchanan in the Arabian Sea.
7 May 1941: Pinguin sank the tanker British Emperor in the Arabian Sea.
8 May 1941: HMS Cornwall sank Pinguin in the Arabian Sea.
10 June 1941: British invasion of Assab as Operation Chronometer.
26 June 1941: German merchant raider Kormoran sank the freighters Velebit and Mareeba in the Bay of Bengal.
25 August 1941: The Royal Navy supported the Anglo-Soviet invasion of Iran.
7 September 1941: Axis aircraft sank the freighter Steel Seafarer in the Red Sea.
24 September 1941: Kormoran sank the freighter Stamatios G. Embiricos in the Arabian Sea.
19 November 1941: Battle west of Australia between HMAS Sydney and Kormoran destroyed both ships.
30 November 1941: Free French forces replaced Vichy French in the battle of La Réunion.
2 December 1941: Convoy BM 9A arrived in Singapore with troops from Colombo.
17 December 1941: Sparrow Force delivered 650 Dutch and Australian troops to Timor.
27 December 1941: Convoy WS 24 arrived in Mumbai with 20,000 troops loaded at Halifax Harbour.
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.