Pacific against the United States, and the Imperial Japanese Army (IJA) refused to allocate troops for an invasion of Ceylon. In response, the IJN developed Operation C, a plan for an aggressive raid into the Indian Ocean in early April. Operation C aimed to destroy the British Eastern Fleet, and disrupt British lines of communications in the Bay of Bengal in support of the Burma Campaign. British intelligence correctly assessed the Japanese strategy. The Americans were notified; the Doolittle Raid – which was already in progress – took on the additional role of a diversion. Japanese preparations Admiral Isoroku Yamamoto issued the initial order to proceed with Operation C to the IJN's southern force, commanded by Admiral Nobutake Kondō, on 9 March 1942. By 16 March, the plan was to depart from Staring Bay, Celebes, on 26 March for an attack on Colombo ("C day") on 5 April. The Japanese expected to destroy the British Eastern Fleet in port. The Japanese force, commanded by Admiral Chūichi Nagumo, had a core of five aircraft carriers; , and in Carrier Division 5, and and in Carrier Division 2. The carriers were accompanied by all four s, and both s. Japanese intelligence on the composition of the British Eastern Fleet in the Indian Ocean was reasonably accurate, while overestimating the air strength on Ceylon. The 19 March operational order vaguely advised that a "considerable" portion of British naval and air forces in the Indian Ocean were "deployed in Ceylon area". The Japanese stationed reconnaissance submarines outside of the known British anchorages at Colombo and Trincomalee; their effectiveness was limited. At least one submarine was sent to scout the Maldive Islands but failed to detect Port T at Addu Atoll. At the same time as Operation C, the IJN also dispatched Malay Force, consisting of the aircraft carrier , six cruisers, and four destroyers to destroy shipping in the Bay of Bengal on 1 April. Malay Force was not part of Operation C. British preparations The reinforcement of the British Eastern Fleet depended on transfers from Britain and the Mediterranean, a reflection of active warzones and the demands on the Royal Navy's (RN) resources. In late-December 1941, a reassessment of the threat posed by Japan envisioned transferring the majority of the RN's heavy units to the Eastern Fleet. Matters were made urgent by the crippling of the United States Pacific Fleet's battle line at