Editing Indian Ocean raid (section)

===British preparations===
[[File:Pacific War - Southern Asia 1942 - Map.jpg|thumb|upright=1|Japanese operation in the Northern Indian Ocean and Bay of Bengal in 1942. Nagumo's forces are shown at the bottom of the map.]]
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 [[Attack on Pearl Harbor|crippling]] of the [[United States Pacific Fleet]]'s battle line at [[Pearl Harbor]], which exposed the weak forces in Malaya to attack. Heavy units were freed up by American reinforcements in the Atlantic. The construction programs of the late-1930s were also starting to yield new heavy units. The Mediterranean yielded far fewer reinforcements than expected due to serious losses in that theatre in 1941.<ref name="Boyd_356">Boyd, p. 356</ref>

The Eastern Fleet that Vice Admiral Sir [[James Somerville (admiral)|James Somerville]] assumed command of in March 1942 was smaller than what had been envisioned in December 1941. Somerville divided the fleet into two groups, based on speed. The faster "Force A" included the [[aircraft carrier]]s {{HMS|Formidable|67|6}} and ''Indomitable'', the modernized [[battleship]] {{HMS|Warspite|03|6}} (as [[flagship]]), as well as the modern cruisers and destroyers. The slower "Force B" was formed around the old carrier {{HMS|Hermes|95|6}} and four unmodernized {{sclass|Revenge|battleship|2}}s. A few [[submarine]]s were also available.<ref name="Boyd_365">Boyd, p. 365</ref><ref name="Boyd_370"/><ref>Somerville, Sir James. [http://www.naval-history.net/xDKWD-EF1942-Introduction.htm ''Report of Proceedings (ROP) Of Eastern Fleet – 1942''] {{Webarchive|url=https://web.archive.org/web/20180228000034/http://naval-history.net/xDKWD-EF1942-Introduction.htm |date=28 February 2018 }}</ref><ref>Roskill, p. 23</ref> The ships had never operated together before, and both ship and air crews were deficient in training.<ref name="Boyd_365"/>

Allied intelligence accurately assessed the strength of the Japanese force.<ref name="Boyd_366"/> Somerville planned to evade the Japanese during the day and close to launch torpedo strikes with [[List of World War II British naval radar#ASV II|radar-equipped]] [[Fairey Albacore]] bombers during the night.<ref name="Boyd_370"/> However, the plan was based on information provided by the [[Far East Combined Bureau]] (FECB), which identified only two carriers in the Japanese force. FECB also believed the Japanese would sail from Staring Bay on 21 March for a "C day" of 1 April. Thus, Somerville sailed early expecting to fight a smaller and manageable enemy force, particularly in aircraft strength.<ref name="Boyd_366"/> As such, Somerville likely did not see his plan as incompatible with his orders from the [[British Admiralty|Admiralty]], which were to protect the lines of communications in the Indian Ocean, and to maintain the Eastern Fleet as a [[fleet in being]] by avoiding unnecessary risks.<ref name="Boyd_366"/>

The British recognized the threat of Japanese carrier-borne air attack on Ceylon after the strike on Pearl Harbor, and the island's air defences were reinforced. On 7 December 1941, air defences consisted of four obsolescent three-inch [[Anti-aircraft warfare|anti-aircraft]] guns – at Trincomalee – with neither fighters nor radar.<ref name="Stuart_2014_33">Stuart 2014, p. 33</ref> By 4 April, there were 67 [[Hawker Hurricane]]s and 44 [[Fairey Fulmar]] fighters, a radar station each at Colombo and Trincomalee, and 144 anti-aircraft guns;<ref name="Stuart_2014_35">Stuart 2014, p. 35</ref> 37 or 38 Hurricanes were serviceable around Colombo on 5 April.<ref name="Stuart_2014_44">Stuart 2014, p. 44</ref> The fighters were divided into three [[Royal Air Force]] (RAF) squadrons of Hurricanes (two at Colombo, and one at Trincomalee), and two squadrons of RN [[Fleet Air Arm]] (FAA) Fulmars.<ref name="Roskill_26"/> In the same time frame, other air forces increased from eight obsolete [[torpedo bomber]]s,<ref name="Stuart_2014_33"/> to seven [[Consolidated PBY Catalina]] flying boats, 14 [[Bristol Blenheim]] IV bombers, and 12 [[Fairey Swordfish]] torpedo bombers.<ref name="Stuart_2014_44"/> On the eve of battle, RAF forces were part of [[No. 222 Group RAF|222 Group]] ([[Air Vice-Marshal]] [[John D'Albiac]]).<ref name="Stuart_2014_37">Stuart 2014, p. 37</ref>