Editing Indian Ocean raid (section)

==Background==
===Strategic situation===
The island of [[Ceylon]] was strategically important, since it commanded the Indian Ocean. Thus it controlled access to India, the vital Allied shipping routes to the [[Middle East]] and the oilfields of the [[Persian Gulf]]. Ceylon held most of the British Empire's resources of [[rubber]]. An important harbour and naval base, [[Trincomalee]], was located on the island's eastern coast. Japanese propaganda had an effect on some of the Sinhalese population, who now awaited their arrival.

The [[fall of Singapore]] on 15 February 1942 broke the United Kingdom's eastern defensive perimeter of the [[Bay of Bengal]]; and the [[Japanese occupation of the Andaman Islands]] on 23 March gave Japan control of the [[Andaman Sea]], enabling ships to resupply Japanese troops in the [[Burma Campaign]] for control of [[India]]. Both German and British authorities anticipated Japanese capture of Ceylon to solidify control of the Bay of Bengal and disrupt British resupply for defence of India, [[Australia]], and perhaps the Middle East. Ceylon was hastily garrisoned by Australian troops returning from North Africa; and {{HMS|Indomitable|R92|6}} was relieved of naval duties to serve as a high-speed aircraft ferry shuttling available planes to Ceylon.<ref>{{cite book |last=Churchill |first=Winston |author-link =Winston Churchill |title =The Hinge of Fate |url=https://archive.org/details/hingeoffate00chur |url-access=registration |publisher =Houghton Mifflin Company |date =1950 |location =Boston |pages =[https://archive.org/details/hingeoffate00chur/page/138 138], 172–178 }}</ref>

Japanese intentions to mount a major offensive into the Indian Ocean were placed on hold in March 1942; strong naval forces were needed in the western 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 [[Far East Fleet (United Kingdom)|Eastern Fleet]], and disrupt British lines of communications in the Bay of Bengal in support of the Burma Campaign.<ref name="Boyd_364">Boyd, p. 364</ref>

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.<ref name="Boyd_364"/>

===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]], [[Sulawesi|Celebes]], on 26 March for an attack on Colombo ("C day") on 5 April.<ref name="Boyd_366">Boyd, p. 366</ref> The Japanese expected to destroy the British Eastern Fleet in port.<ref name="Boyd_381">Boyd, p. 381</ref>

The Japanese force, commanded by Admiral [[Chūichi Nagumo]], had a core of five aircraft carriers; {{Ship|Japanese aircraft carrier|Akagi||2}}, {{Ship|Japanese aircraft carrier|Shōkaku||2}} and {{Ship|Japanese aircraft carrier|Zuikaku||2}} in Carrier Division 5, and {{Ship|Japanese aircraft carrier|Sōryū||2}} and {{Ship|Japanese aircraft carrier|Hiryū||2}} in Carrier Division 2.<ref name="Boyd_373">Boyd, p. 373</ref> The carriers were accompanied by all four {{sclass|Kongo|battleship|2}}s, and both {{sclass|Tone|cruiser|2}}s.<ref name="Boyd_367">Boyd, p. 367</ref>

Japanese intelligence on the composition of the British Eastern Fleet in the Indian Ocean<ref name="Tully_Yu_5">Tully and Yu, p. 5</ref> was reasonably accurate, while overestimating the air strength on Ceylon.<ref name="Boyd_381">Boyd, p. 381</ref> 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".<ref name="Tully_Yu_5"/>

The Japanese stationed reconnaissance submarines outside of the known British anchorages at Colombo and Trincomalee; their effectiveness was limited.<ref name="Boyd_369">Boyd, p. 369</ref> At least one submarine was sent to scout the [[Maldive Islands]] but failed to detect [[Gan (Addu Atoll)|Port T]] at [[Addu Atoll]].<ref name="Boyd_370">Boyd, p. 370</ref>

At the same time as Operation C, the IJN also dispatched Malay Force under the command of Vice Admiral [[Jisaburō Ozawa]]. His force consisted of the aircraft carrier {{Ship|Japanese aircraft carrier|Ryūjō||2}}, six [[cruiser]]s, and four destroyers to destroy shipping in the Bay of Bengal on 1 April. Malay Force was not part of Operation C.<ref>Shores, Cull & Izawa, Vol. II, pp. 393, 408–411</ref>

In 3 days, Ozawa's force managed to sink 23 merchant ships (20 in a single day),<ref name=":0">{{Cite journal |last=Black |first=Jeremy |date=2009 |title=Midway and the Indian Ocean |url=https://www.jstor.org/stable/26397057 |journal=Naval War College Review |volume=62 |issue=4 |pages=135 |jstor=26397057 |issn=0028-1484 |archive-date=4 January 2024 |access-date=4 January 2024 |archive-url=https://web.archive.org/web/20240104040347/https://www.jstor.org/stable/26397057 |url-status=live }}</ref> totaling over 130,000 gross registered tons.{{sfn|Warner|Bennett|Macyntire|Uehling|1976|p=154}} In addition, April saw 32,000 tons of shipping sunk by Japanese submarines off India's west coast.<ref name=":0" /> ''Ryūjō''{{'}}s aircraft also bombed the ports of [[Cocanada]] and [[Vizagapatam]], causing relatively minor damage.<ref name=":0" /> The tonnage and number of ships sunk by Malay Force, are comparable to that of the 3-month long [[Operation Berlin (Atlantic)|Operation Berlin]] raid conducted by [[Scharnhorst-class battleship|two battleships]] of the ''[[Kriegsmarine]]'' from January to March 1941.{{sfn|Macintyre|1975|pp=104–106}} In both raids against merchant shipping, Allied merchant ships were not sailing in convoys escorted by large vessels.{{sfn|Ireland|2004|p=48}}

===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>