Indian Ocean raid


The Indian Ocean raid, also known as Operation C or Battle of Ceylon in Japanese, was a naval sortie carried out by the Imperial Japanese Navy from 31 March to 10 April 1942. Japanese aircraft carriers under Admiral Chūichi Nagumo struck Allied shipping and naval bases around British Ceylon, but failed to locate and destroy the bulk of the British Eastern Fleet. The Eastern Fleet, commanded by Admiral Sir James Somerville, was forewarned by intelligence and sailed from its bases prior to the raid; its attempt to attack the Japanese was frustrated by poor tactical intelligence.
Following the attack, the British expected a major Japanese offensive in the Indian Ocean. The main base of the Eastern Fleet relocated to East Africa, and Ceylon was reinforced, but Somerville kept his fast carrier division, Force A, "in Indian waters, to be ready to deal with any attempt by the enemy to command those waters with light forces only." However, the Japanese had no short-term plans to follow up on their success, and within the year operations in the Pacific made it impossible to do so.

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 was relieved of naval duties to serve as a high-speed aircraft ferry shuttling available planes to Ceylon.
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 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 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 under the command of Vice Admiral Jisaburō Ozawa. His force consisted 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.
In 3 days, Ozawa's force managed to sink 23 merchant ships, totaling over 130,000 gross registered tons. In addition, April saw 32,000 tons of shipping sunk by Japanese submarines off India's west coast. Ryūjōs aircraft also bombed the ports of Cocanada and Vizagapatam, causing relatively minor damage. The tonnage and number of ships sunk by Malay Force, are comparable to that of the 3-month long Operation Berlin raid conducted by two battleships of the Kriegsmarine from January to March 1941. In both raids against merchant shipping, Allied merchant ships were not sailing in convoys escorted by large vessels.

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 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 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.
The Eastern Fleet that Vice Admiral Sir 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 carriers and Indomitable, the modernized battleship , as well as the modern cruisers and destroyers. The slower "Force B" was formed around the old carrier and four unmodernized s. A few submarines were also available. The ships had never operated together before, and both ship and air crews were deficient in training.
Allied intelligence accurately assessed the strength of the Japanese force. Somerville planned to evade the Japanese during the day and close to launch torpedo strikes with radar-equipped Fairey Albacore bombers during the night. However, the plan was based on information provided by the Far East Combined Bureau, 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. As such, Somerville likely did not see his plan as incompatible with his orders from the 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.
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 guns – at Trincomalee – with neither fighters nor radar. By 4 April, there were 67 Hawker Hurricanes and 44 Fairey Fulmar fighters, a radar station each at Colombo and Trincomalee, and 144 anti-aircraft guns; 37 or 38 Hurricanes were serviceable around Colombo on 5 April. The fighters were divided into three Royal Air Force squadrons of Hurricanes, and two squadrons of RN Fleet Air Arm Fulmars. In the same time frame, other air forces increased from eight obsolete torpedo bombers, to seven Consolidated PBY Catalina flying boats, 14 Bristol Blenheim IV bombers, and 12 Fairey Swordfish torpedo bombers. On the eve of battle, RAF forces were part of 222 Group.

Raid

First moves

The Japanese sailed from Staring Bay on 26 March as planned. Somerville sailed on 30 March in expectation of an attack on 1 April, and deployed his fleet in a patrol area south of Ceylon. Ceylon air defences and forces went on alert, with land-based aerial reconnaissance concentrating on the southeast, where the Japanese were expected to approach to launch strikes at Colombo and Trincomalee. Late on 2 April, the British retired toward Port T – southwest of Ceylon – to refuel. Somerville also detached various ships to resume previous commitments; the heavy cruisers and were sent to Colombo, and Hermes to Trincomalee. Air defences stood down, although Catalina patrols continued.
At about 16:00 on 4 April, PBY Catalina flying boat from the Royal Canadian Air Force's 413 Squadron flown by Squadron Leader Leonard Birchall spotted Nagumo's fleet south-east of Ceylon on a course that would have entered Somerville's previous patrol area from the south. The Catalina transmitted the sighting, but not the size of the fleet, before being shot down. At this time, Somerville was refuelling at Port T; Force A sailed eastward toward the Japanese upon receiving the sighting; Force B could not be ready until 5 April. Catalina FV-R from 205 Squadron RAF took off at 17:45 to shadow the Japanese fleet, making its first report at 22:37 on 4 April, and a final report at 06:15 on 5 April while from Ceylon. FV-R was shot down about 90 minutes after the final report.
Within an hour of QL-A's report, D'Albiac met with his subordinates to discuss an anticipated Japanese strike after dawn. 222 Group issued a warning to subordinate units before midnight, and units went on alert at 04:00 on 5 April. On the morning of 5 April, six Swordfish from 788 Naval Air Squadron began relocating from China Bay, near Trincomalee, to Colombo, in preparation for a strike on the Japanese fleet. Admiral Geoffrey Layton, on Ceylon, ordered ships put to sea to avoid being attacked in harbour. Cornwall and Dorsetshire, which had just reached Colombo, were sent to rejoin Force A; they sailed late on 4 April. Hermes sailed from Trincomalee and was ordered to hide northeast of Ceylon.
The Japanese did not perform an aerial reconnaissance sweep along their intended course on the afternoon of 4 April, and a planned reconnaissance of Colombo harbour by cruiser floatplanes was cancelled. The Japanese realized surprise was lost after intercepting a signal from Colombo asking QL-A to repeat its report.