Indian Ocean raid

Ceylon The island of Ceylon commanded the Indian Ocean, controlling access to India, the Allied shipping routes to the Middle East and the oilfields of the Persian Gulf. After the fall of British Malaya, Ceylon became the source of most of the British Empire's rubber. The harbour and naval base, Trincomalee is on the east coast. Japanese propaganda had an effect on some of the Sinhalese population, who awaited their arrival. The fall of Singapore on 15 February 1942 broke the British 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 supply Japanese troops in the Burma Campaign. German and British authorities anticipated the Japanese capture of Ceylon to consolidate control of the Bay of Bengal and disrupt British supply for the defence of India, Australia and perhaps the Middle East. Ceylon was hastily garrisoned by Australian troops returning from North Africa and was used as a high-speed aircraft ferry, shuttling fighter aircraft to Ceylon. A Japanese offensive into the Indian Ocean were postponed in March 1942; the IJN was needed in the western Pacific against the United States and the Imperial Japanese Army (IJA) refused to allocate troops for an invasion of Ceylon. The IJN planned a lesser effort, Operation C, a raid into the Indian Ocean in early April. C aimed to destroy the British Eastern Fleet and disrupt British communications in the Bay of Bengal in support of the Burma Campaign. British intelligence uncovered the Japanese plan, the Americans were notified and the Doolittle Raid took on the additional role of a diversion. Japanese preparations Admiral Isoroku Yamamoto issued the order to proceed with Operation C to the southern force of the IJN (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 to catch the Eastern Fleet in port. The Japanese force, commanded by Admiral Chūichi Nagumo, had 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 Eastern Fleet 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 submarines outside of the British anchorages at Colombo and Trincomalee to keep watch but their effectiveness was limited. At least one submarine went to scout the Maldive Islands but failed to detect that Gan (Port T) at Addu Atoll was a fleet fuelling base. Malay Force Concurrent with Operation C, the IJN dispatched Malay Force (Vice Admiral Jisaburō Ozawa) on a raid in the Bay of Bengal. The force departed from Mergui (now Myeik, Myanmar) on 1 April consisting of the aircraft carrier , six cruisers, a light cruiser and four destroyers. The Eastern Fleet was far to the south, operating against Operation C and the British were incapable of defending the merchant ships in the Bay, having only a couple of Indian sloops and the Greek destroyer ; merchant ships sailed in small groups and hugged the coast. On 5 April, at 16°N, 88°E, the force divided into North, centre and South units to search for targets south of False Point (20°20′N, 86°44′E) and Cocanada. On 5 April aircraft from Ryūjō sank a ship and Calcutta (now Kolkata) where ships had begun dispersing on 31 March, cancelled sailings on 6 April. On 6 April, aircraft from Ryūjō bombed the coastal towns of Cocanada and Vizagapatam causing minor damage and a panic that led to an exodus from both places. In three days, Malay Force managed to sink 20 merchant ships and damage three more of over in attacks by aircraft and ships. On the eastern side off the Bay, off Akyab (now Sittwe) in Burma at 20°7′N, 92°54′E, the Burma Coast Force was attacked by land-based aircraft and lost a with ten men wounded. During the chaos caused by Operation C and the raid by Malay Force, the Japanese were able to get a convoy of troops and equipment into Rangoon. Another 32,000 GRT of shipping was sunk by Japanese submarines off the west coast of Indiat during the month. British preparations The reinforcement of the Eastern Fleet depended on transfers from Britain and the Mediterranean. In late December 1941, a reassessment of the threat posed by Japan envisioned the Navy transferring the majority of the big ships to the Eastern Fleet. Matters were made urgent by the Attack on Pearl Harbor that sank much of the United States Pacific Fleet, that exposed the weak forces in Malaya to attack. Heavy units were freed by American reinforcements in the Atlantic. The pre-war rearmament was beginning to yield more big ships. The Mediterranean Fleet transferred far less reinforcements than expected due to its losses in 1941. Vice Admiral Sir James Somerville assumed command of an Eastern Fleet in March 1942 that was smaller than envisioned in December 1941. Somerville divided the fleet into a fast Force A with the aircraft carriers and Indomitable, the modernised battleship (as flagship), as well as the modern cruisers and destroyers. Force B was formed around the old carrier and four un-modernised s; a few submarines were also available. The ships had not operated together before and 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 at night close for torpedo attacks with radar-equipped Fairey Albacore bombers. The plan was based on information from 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 and that C day was 1 April. Somerville sailed early, expecting to fight a smaller Japanese force, particularly in aircraft strength. Somerville had orders from the Admiralty, to protect the communications in the Indian Ocean and to keep the Eastern Fleet in being by avoiding risks. After the attack on Pearl Harbor the Ceylon air defences were reinforced. On 7 December 1941, the air defences consisted of four obsolescent three-inch anti-aircraft guns at Trincomalee with no fighters or radar. By 4 April, there were 67 Hawker Hurricanes and 44 Fairey Fulmar fighters, radar station at Colombo and Trincomalee and 144 anti-aircraft guns. There were 37 or 38 operational Hurricanes around Colombo on 5 April in three RAF squadrons, two at Colombo and one at Trincomalee. There were two squadrons of RN Fleet Air Arm (FAA) Fulmars. Other squadrons 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 (Air Vice-Marshal John D'Albiac). ==Raid==

26 March−3 April The Japanese sailed from Staring-baai (Staring Bay) on 26 March as planned. Somerville sailed on 30 March, expecting an attack on 1 April and took the fleet to a patrol area south of Ceylon. Ceylon air defences and forces went on alert, with land-based aerial reconnaissance concentrating on the south-east, where the Japanese were expected to approach for attacks on Colombo and Trincomalee. Late on 2 April, the Eastern Fleet retired toward Port T south-west of Ceylon to fuel. Somerville detached several ships to resume their commitments; the heavy cruisers and were sent to Colombo and Hermes to Trincomalee. The air defences stood down, except for Catalina patrols. 4 April At about 16:00 on 4 April, PBY Catalina flying boat (AJ155/QL-A) from 413 Squadron, Royal Canadian Air Force (RCAF) flown by Squadron Leader Leonard Birchall spotted the Combined Fleet south-east of Ceylon on a course that would have entered the British fleet patrol area from the south. The Catalina transmitted the sighting but not the size of the fleet before being shot down. Somerville was refuelling at Port T; Force A sailed eastwards toward the Japanese upon receiving the sighting; Force B could not be ready until 5 April. Catalina FV-R from 205 Squadron 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 to brief his staff on an anticipated Japanese attack after dawn and 222 Group issued a warning and units went on alert at 04:00 on 5 April. On the morning of 5 April, six Swordfish from 788 Naval Air Squadron (788 NAS) flew from China Bay, near Trincomalee, to Colombo, to be ready for an attack on the Japanese fleet. Admiral Geoffrey Layton, at Ceylon, ordered ships to disperse from harbour. Cornwall and Dorsetshire, that had just reached Colombo, were sent back towards Force A late on 4 April. Hermes sailed from Trincomalee and was ordered to hide north-east of Ceylon. The Japanese did not perform an aerial reconnaissance along their intended course on the afternoon of 4 April, and a planned reconnaissance of Colombo harbour by cruiser seaplanes was cancelled. The Japanese intercepted a signal from Colombo asking QL-A to repeat its report, showing that they had lost surprise . 5 April Japanese intelligence on the morning of 5 April 1942 indicated that British carriers were absent and the Japanese morning air search was limited accordingly. At dawn, Japanese aerial reconnaissance aircraft flew off to the south-west and north-west; they would fly out to a maximum of over the next few hours. A reconnaissance Fulmar launched from Force A at 08:00 spotted one of the Japanese aircraft at the extreme edge of the south-west search area at 08:55 about ahead of Force A. Shortly after 06:00 91 Japanese bombers and 36 fighters began taking off for the attack on Colombo. British early warning failed to detect and identify the incoming strike, forcing British pilots to scramble under fire when the first Japanese aircraft appeared over them at 07:45. The defence Ratmalana airfield by British fighters left the harbour undefended. The armed merchant cruiser , the Norwegian tanker Soli and the old destroyer were sunk; three other ships were damaged. The port was damaged but was not put out of action. Twenty of the 41 British fighters that took off were shot down. At least one fighter was damaged taking off and crashed. The six Swordfish of 788 NAS arrived during the battle and were shot down. The Japanese lost seven aircraft. Nagumo changed course to west-south-west at 08:30, unknowingly causing the opposing fleets to steam toward one another and recovered the Colombo strike from 09:45 to 10:30. The size of the attack on Colombo was Somerville's first evidence that the Japanese force had more than the expected two carriers; he continued to steam toward the Japanese fleet at . Radar-based fighter direction would allow Force A to avoid surprise attack by neutralising shadowing Japanese aircraft. Loss of Dorsetshire and Cornwall At 10:00, an aircraft from Tone searching the southwest area spotted and began shadowing Dorsetshire's force; the aircraft reported that the cruiser was heading south-west and making . The cruisers reported the shadower but had no means to drive it off. Nagumo increased speed from upon receiving the sighting. Carrier Division 5's reserve strike force was ordered to rearm with torpedoes, replacing the bombs intended for a second attack on Colombo. The rearming was too slow and Carrier Division 2 attacked instead. Soryu and Hiryu began launching dive bombers at 11:45. Radar of Force A detected the attack on the cruisers at 13:44, putting the aircraft to the north-east. Cornwall and Dorsetshire were sunk at 14:00 and 424 officers and crew were lost. The Japanese did not find Force A after sinking the cruisers. Had aircraft shadowing the cruisers flown another along the cruisers' course before returning to Tone, it would have detected Force A if it had flown south-west for another ten minutes. Nagumo recovered the attacking aircraft at 14:45. 5 April, afternoon Somerville launched four Albacores from Indomitable at 14:00 to search an arc to the north-east out to . Nagumo's south-easterly course would have taken the Japanese fleet right through the centre of the arc. At 15:00 or 15:30, Nagumo changed course to the south-west. Carrier Division 2 did not immediately follow; it performed a series of kinking manoeuvres starting at 15:00 that initially took it north-west. Carrier Division 2 was spotted by the two northerly Albacores around 16:00. Hiryū launched Mitsubishi A6M Zero fighters to intercept the scouts; one Albacore was damaged at 16:04, and the other shot down at 16:28 without reporting. The two southern-most Albacores missed Nagumo's main body. Somerville did not receive the damaged Albacore's sighting report until 16:55; the report gave the position of Carrier Division 2 with reasonable accuracy, placed the Japanese away, but contained no other data. At 17:00 he received signals intelligence (SIGINT) from Colombo reporting the Japanese course at 14:00 as south-westerly, at . Somerville ordered a course change to the southwest at 17:26, not knowing that Nagumo's main body was away, and that Carrier Division 2 was only away. The course change was presumably to maintain distance between a superior enemy that was believed to be still closing, or to cover Port T from attack, but it also meant the British lost an opportunity to meet the enemy; had Force A continued on its easterly course, Carrier Division 2 would have passed right in front of it at 21:00 at range of about . The damaged Albacore landed at 17:45, less than a half-hour before sunset and the crew was debriefed. There were two revisions to the 16:00 sighting, which were transmitted to Somerville at 18:00 and 18:17 respectively and differed significantly from each other and the original report. The final revision correctly identified the two carriers of Carrier Division 2 but also claimed they were heading toward the north-west at a position or the original sighting. The course heading conflicted with the first revision, which suggested a course toward the south-east. Late on 5 April, FECB decrypted a JN 25B message containing Nagumo's planned movement on 6 April, but this did not aid Somerville as the transmission to the fleet was garbled. Somerville declined to launch a strike based on poor information and opted to head north-west in pursuit. One radar-equipped aircraft was launched to search a northern arc out to . Aircraft were sent later to search the easterly arc but it was too late to re-gain contact with the Japanese. For the Japanese, too, there was a lost opportunity to find the British before night fell. Nagumo did not order a search for the British carriers at the appearance of British carrier-based aircraft. Search aircraft might require homing signals from the carriers to return, that the British could use to locate the Japanese. The Japanese fleet continued south-east at ignorant of the presence of Force A. Carrier Division 2 rejoined the main body's track at 18:00 and caught up at 22:00 due east of Force A. The Japanese circled wide to the south and then east in preparation for an attack on Trincomalee. The Japanese suspected the presence of British carriers and on the morning of 6 April they launched a much denser westwards air search but still found nothing. Further searches on route to Trincomalee were equally unsuccessful as the British carriers were by that time far to the west. 6–8 April By 6 April, FECB decrypts of Japanese wireless codes indicated the force contained four carriers and three battleships, that Somerville realised was beyond the capacity of the Eastern Fleet to engage without undue risk. The declining serviceability of his fighter force also reinforced his caution. Somerville did not immediately withdraw or return to port; Force B rejoined early on 6 April. In the afternoon 1,122 survivors from Dorsetshire's force were recovered, while maintaining a look-out for the Japanese force with all-around air reconnaissance. Intelligence from Ceylon put the Japanese between Port T and Ceylon. Somerville cautiously arrived at Port T from the west at 11:00 on 8 April and refuelled. By 8 April, the Eastern Fleet had withdrawn and the Japanese fleet was approaching Trincomalee from the east. The Japanese fleet was detected by a RAF Catalina at 15:17 on 8 April and the harbour at Trincomalee was cleared that night. Hermes, escorted by , was sent south along the coast. 9 April The Japanese air search on the morning of 9 April was limited as British carriers were no longer expected. The Japanese strike group of 132 aircraft was detected at 07:06 by AMES 272 from Trincomalee. The RAF and FAA scrambled 17 Hurricanes and six Fulmars in good time and a section of Hurricanes, already airborne on dawn patrol, attacked three Zeroes and shot down two. The China Bay airfield and the port were severely bombed and the monitor was damaged. () a merchant ship carrying aircraft and ammunition was set on fire and abandoned, with two men killed of 138 crew; eventually the hulk drifted into Malay Cove. Eight Hurricanes and a Fulmar were shot down and several unserviceable aircraft were destroyed on the ground; the Japanese lost four aircraft. At 07:16 another Catalina from 413 Squadron RCAF spotted the Japanese fleet and was shot down while reporting. Around 10:25, nine un-escorted Blenheims from 11 Squadron attacked Nagumo's force and eluded the combat air patrol (CAP). Hiryū spotted the aircraft but failed to relay a warning to the other ships and the attack achieved surprise. The bombers attacked Akagi at and the bombs fell close to Hiryū but none hit. Four Blenheims were shot down after they had bombed and turned for home by Zeros of the standing patrol, two claimed by Kaname Harada and another by Japanese aircraft returning from the attack on Hermes. A Zero was shot down near the carriers and another in the formation returning from Trincomalee. This was the first time a Japanese carrier force had faced a concerted air attack. Hermes and Vampire were away when Trincomalee was attacked. At 09:00 they reversed course. Shortly after the attack on Trincomalee ended, a reconnaissance aircraft from spotted the ships. Eighty Aichi D3A Val bombers, held in reserve on the Japanese carriers, began an attack at 10:35 and the ships were sunk off Batticaloa before noon. Hermes was hit by over forty bombs and sank with the loss of 307 men; eight of the crew on Vampire were killed. The nearby hospital ship was not attacked as it rescued 600 survivors. Aircraft from Soryu attacked , a that was escorting and sank the corvette with the loss of 53 men. The tanker and the cargo ship were also sunk. British Fulmars arrived from Trincomalee too late to help Hermes but shot down four Vals for the loss of two of the Fulmars. Nagumo disengaged after recovering the strike on Hermes. ==Aftermath==

Analysis The Japanese failed to find the bulk of the Eastern Fleet and the British overestimated the danger to Ceylon and the Eastern Fleet, that safeguarded the sea lines of communications. Signals intelligence suggested that the Japanese were preparing a deliberate advance across the Indian Ocean. The raid demonstrated that the RAF was too weak to defend Ceylon and that the navy was ill-prepared to meet a Japanese carrier force. The Eastern Fleet withdrew to Kilindini at Mombasa in East Africa Protectorate (Kenya) temporarily abandoning the eastern Indian Ocean to Japan; from there it contested control of the central Indian Ocean on better terms. Force A, with its two aircraft carriers, retired to Bombay and Somerville regularly sent a fast carrier force to the central Indian Ocean over the next six months, during which he operated from or near Ceylon for about half that time. On 18 April, the Eastern Fleet was accorded the highest priority for reinforcement, including the transfer of most of the carriers from the Home Fleet and the Mediterranean Fleet, intending to return to Ceylon in September. By June, Ceylon had three RAF fighter squadrons (64 aircraft, plus reserves) three anti-shipping squadrons (including one of Beaufort torpedo bombers) and much improved radar and anti-aircraft defences. The ground defences were manned by two Australian army brigades but the invasion scare was short-lived. British intelligence detected the movement of the Japanese carrier force eastwards in mid-April and its arrival in the Pacific in mid-May. After the Battle of Midway in June, the threat of serious Japanese naval activity in the Indian Ocean ended. In September, British intelligence predicted Japan would go over to the defensive; the reinforcement of the Eastern Fleet stopped and it was reduced in size in late July. Somerville took risks with the fleet, including the deployment of the fleet on 30 March. Somerville relied on radar sets, that had inexperienced operators, to find the Japanese fleet for a night attack. If the Japanese approached as expected from the south-east and the British failed to find them before dawn, the two fleets would be about apart. The British could be detected by Japanese aerial reconnaissance at sunrise and be subjected to air attacks all day. The British would have been just as vulnerable had they still been on station when the Japanese arrived from the south-west. The failure of the Japanese fleet to appear on 1–2 April led Somerville mistakenly to believe that all of the Allied intelligence on Operation C was flawed. He detached Cornwall, Dorsetshire and Hermes, that were sunk in areas overflown by Japanese aerial reconnaissance. Re-fuelling at Port T a few days later, rather than at Ceylon on 2 April, kept the British away from the Combined Fleet and perhaps saved the Eastern Fleet. Andrew Boyd wrote that Somerville and the Admiralty broadly agreed. Somerville faced challenges not apparent in the Atlantic or Mediterranean. Japanese air superiority made it difficult to scout, close and attack during the day. Radar-enabled night attack was the only alternative but this was risky; careful positioning, luck and Japanese errors nearly produced the conditions for an attack on the night of 5/6 April. The Combined Fleet was within , an hour away in an Albacore but information on the Japanese vector was missing. Even then, it required experienced air crews to find their targets at night using new tactics and radar sets with the short range of . The Japanese did not exploit their victory as the British feared. The aircraft carriers needed maintenance and replenishment after months of intensive operations and there was already difficulties in maintaining the strength of frontline air units. Nagumo and officers such as Mitsuo Fuchida (commander of the Akagi air group) felt that the losses inflicted on the British did not justify the loss of experienced Japanese air crews. Japanese attention also lay elsewhere; in early May the aircraft carriers fought the Battle of the Coral Sea in the south-west Pacific, followed in June by the Battle of Midway. In June, the IJA planned an offensive in the Indian Ocean, including an invasion of Ceylon. The Germans were advancing in North Africa, that made an Axis meeting in the Middle East an attractive proposition. The IJN rejected plan, especially after the beginning of the Guadalcanal campaign (7 August 1942 – 9 February 1943). Henceforth, Japanese operations in the Indian Ocean were against trade, with submarines and armed merchant cruisers. Submarines patrolling off East Africa attacked the harbour at Diego-Suarez in Madagascar during the Allied invasion Battle of Madagascar (5 May – 6 November 1942). The Allies wanted to forestall the Japanese to prevent them from establishing a base on Madagascar to attack shipping. Japanese attacks on merchant ships had some success but after 1942 the IJN could not contest the control of the Indian Ocean. In 2017, Andrew Boyd called Nagumo's leadership rigid and unimaginative, contributing to the escape of the Eastern Fleet. The manoeuvring of his fleet was mainly to facilitate strikes on Colombo and Trincomalee; the possibility that the British might be at sea was apparently not seriously considered. He failed to appreciate that the direction that Dorsetshires force was sailing and the later appearance of British carrier-based aircraft, were related. Inadequate aerial reconnaissance provided Nagumo with little information of what was around him, especially to his front and exposed flanks. He was not well served by the confidence that there was nothing else to be found outside of the few searches made. The limited air searches conducted at the start of the battle reflected contemporary IJN practice, where the intensity of air searches was determined according to expected threats. More aircraft were devoted to the morning search on 6 April, reflected suspicion that British carriers might be present. The intensity of later air searches dropped off when the British carriers were not found and there was little expectation of encountering them. Ultimately, all navies suffered from inadequate air search planning during this period. Inadequate aerial reconnaissance failed to locate the Eastern Fleet in time, there was difficulty in the rearming aircraft at short notice and the lack of radar-directed fighter control allowed the Blenheims to evade the CAP by the Blenheims and this happened again at the Battle of Midway (4–7 June 1942). Casualties The Japanese damaged port facilities, sank one carrier and two cruisers, destroyed a third of enemy ground-based fighters and nearly all of the ground-based anti-shipping aircraft. The Japanese sank 23 merchant ships, totalling 112,312 GRT including those by the Malay Force raid further north in the Bay of bengal, concurrent with Operation C. The Japanese lost 18 aircraft, six fighters, ten dive-bombers and two bombers and about 31 more damaged. ==Japanese order of battle==

Japanese aircraft Ships sunk, 5 April 1942 Ships sunk, 9 April 1942 Malaya Unit Striking Force Replenishment ships Malaya Force groups Ships sunk by Malaya Force ==British order of battle (Ceylon)==

Army Royal Air Force, Fleet Air Arm Eastern Fleet Eastern Fleet aircraft ==Footnotes==