At the beginning of March 1942, "Royal Sovereign", the heavy cruiser , and several smaller vessels escorted the convoy SU.1 of twelve troopships transporting 10,090 soldiers. The convoy departed Colombo on 1 March, bound for Australia. The convoy reached Fremantle without incident on 15 March. By the end of March 1942, the Eastern Fleet had been formed, under the command of Admiral James Somerville. The fleet was centred on a pair of fleet aircraft carriers, the elderly carrier , and five battleships, four of which were "Royal Sovereign" and her sisters; the fifth was "Warspite". The fleet also included seven cruisers and sixteen destroyers. Despite the numerical strength of the Eastern Fleet, many of its units, including the four "Revenge"-class battleships, were no longer front-line warships. Vice Admiral Chūichi Nagumo's powerful "Kido Butai", composed of six carriers and four fast battleships, was significantly stronger than Somerville's Eastern Fleet. As a result, only the modernised "Warspite" could operate with the two fleet carriers; "Royal Sovereign", her three sisters, and "Hermes" were kept away from combat to escort convoys in the Indian Ocean. In late March, the code-breakers at the Far East Combined Bureau, a branch of Bletchley Park, informed Somerville that the Japanese were planning a raid into the Indian Ocean to attack Colombo and Trincomalee and destroy his fleet. He therefore divided his fleet into two groups: Force A, which consisted of the two fleet carriers, "Warspite" and four cruisers, and Force B, centred on "Royal Sovereign" and her sisters and the carrier "Hermes". He intended to ambush Nagumo's fleet in a night action, the only method by which he thought he could achieve a victory. After three days of searching for the Japanese fleet without success, Somerville returned to Addu Atoll to refuel. While refuelling his ships, Somerville received a report that the Japanese fleet was approaching Colombo, which they attacked the following day, on 5 April, followed by attacks on Trincomalee on 9 April. Following the raid in April 1942, Somerville withdrew "Royal Sovereign" and her three sisters to Mombasa, where they could secure the shipping routes in the Middle East and the Persian Gulf. "Royal Sovereign" and her sisters departed from Addu Atoll early on the morning on 9 April, bound for Mombasa. Here they remained stationed until September 1943, with the exception of another long period in the dockyard in Philadelphia in late 1942.