The Eastern Fleet, later called the East Indies Fleet, was a fleet of the Royal Navy which existed between 1941 and 1952.

In 1904, the British First Sea Lord, Admiral Sir John Fisher, ordered that in the event of war the three main commands in the Far East, the East Indies Squadron, the China Station, and the Australian Squadron, should all come under one command called the Eastern Fleet based in Singapore. The Commander-in-Chief, China would then take command. During the First World War, the squadrons retained their distinct identities and 'Eastern Fleet' was used only as a general term. The three-squadron structure continued until the Second World War and the beginning of hostilities with the Empire of Japan, when the Eastern Fleet was formally constituted on 8 December 1941, amalgamating the East Indies Squadron and the China Squadron.

During the war, it included many ships and personnel from other navies, including those of the Netherlands, Australia, New Zealand, and the United States. On 22 November 1944 the Eastern Fleet was re-designated East Indies fleet and continued to be based in Trincomalee. Following its re-designation its remaining ships formed the British Pacific Fleet. In December 1945 the British Pacific Fleet was disbanded and its forces were absorbed into the East Indies fleet. In 1952 the East Indies Fleet was renamed the Far East Fleet.

Until the Second World War, the Indian Ocean had been a British "lake". It was ringed by significant British and Commonwealth possessions and much of the strategic supplies needed in peace and war had to pass across it: i.e. Persian oil, Malayan rubber, Indian tea, Australian and New Zealand foodstuffs. Britain also used Australian and New Zealand manpower; hence, safe passage for British cargo ships was critical.

At the outbreak of war, Nazi Germany's Kriegsmarine used auxiliary cruisers (converted merchant ships) and the "pocket battleship" Admiral Graf Spee to threaten the sea lanes and tie down the Royal Navy. In mid-1940, Italy declared war and their vessels based in Italian East Africa posed a threat to the supply routes through the Red Sea. Worse was to come when the Japanese declared war in December 1941 and, after Pearl Harbor, the sinking by air attack of the battleship Prince of Wales and battlecruiser Repulse, and the occupation of Malaya, Singapore and the Dutch East Indies, there was an aggressive threat from the east.

This threat became a reality during the Indian Ocean raid when an overwhelming Japanese naval force operated in the eastern Indian Ocean, sinking an aircraft carrier and other warships, and disrupting freight traffic along the Indian east coast. At this stage, the Chief of the Imperial General Staff, General Sir Alan Brooke wrote of the situation in 14 April 1942:

We were at the time literally hanging on by our eye-lids! Australia and India were threatened by the Japanese, we had temporarily lost control of the Indian Ocean, the Germans were threatening Iran and our oil, Auchinleck was in precarious straits in the desert, and the submarine sinkings were heavy.

Until 1941, the main threat to British interests in the region was the presence of German commerce raiders (auxiliary cruisers) and submarines. The fleet had trade protection as its first priority and was required to escort convoys and eliminate the raiders. The Germans had converted merchant ships to act as commerce raiders and allocated supply ships to maintain them. The location and destruction of these German raiders consumed much British naval effort until the last raider – Michel – was sunk in October 1943.