Indian Ocean raid

• 1. Introduction

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  The Indian Ocean raid, known to the Japanese as Operation C, lasted just eleven days in April 1942, yet it shook the foundations of British imperial power in Asia. Five aircraft carriers under Admiral Chuichi Nagumo swept out of Staring Bay in the Celebes on the 26th of March, bound for Ceylon and the Eastern Fleet anchored there. The British had cracked Japanese codes and knew the attack was coming. Their fleet sailed before Nagumo arrived. What followed was a game of near-misses, catastrophic sinkings, and strategic blunders on both sides that would shape the Indian Ocean for the rest of the war. How did the British avoid losing their entire Eastern Fleet in a single week? Why did Japan, after inflicting serious losses, simply turn around and go home? And what did it mean for an empire already reeling from Singapore, Burma, and the Dutch East Indies?

• 2. Ceylon on the Eve

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  In the 1930s, more shipping tonnage passed through Ceylon than through all the ports of India combined. The island sits directly across the sea lanes connecting Singapore and Rangoon to the Red Sea and the Persian Gulf, making Colombo and Trincomalee two of the most strategically vital harbours in the world. When the Pacific War began on the 7th of December 1941, that geography became a liability as much as an asset.

  The fall of Singapore on the 15th of February 1942 drove hundreds of ships into Colombo Harbour. A port built for 45 ships was soon holding 100 to 110 at once. The British eastern defensive perimeter had collapsed. Japan seized the Andaman Islands on the 23rd of March, giving its forces control of the Andaman Sea and a direct supply corridor to its army in Burma. Ceylon now stood exposed.

  Garrisoning the island was improvised at speed. Australian troops returning from North Africa were rerouted there. By June 1942 the garrison had grown by thousands, with troop movements tracked in waves across the preceding months. The civilian workforce, some 3,600 civil engineers, had already converted from peacetime tasks to repairing ships and building dummy aircraft, guns, and radar installations. Air defences on the 7th of December 1941 had consisted of four obsolescent three-inch anti-aircraft guns at Trincomalee and no fighters at all. By the 4th of April there were 67 Hawker Hurricanes, 44 Fairey Fulmars, radar stations at both major ports, and 144 anti-aircraft guns. The transformation was real, but the question of whether it was enough would be answered on the 5th of April.

• 3. Intelligence and Miscalculation

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  Admiral Isoroku Yamamoto issued the order for Operation C on the 9th of March 1942. By the 16th of March the plan was fixed: the Kido Butai, the 1st Air Fleet, would depart Staring Bay on the 26th of March and strike Colombo on the 5th of April, catching the Eastern Fleet in port. The Japanese sent submarines to watch Colombo and Trincomalee, and reconnoitred the Maldives by submarine. But they missed one critical detail: Gan, known as Port T, was a fleet fuelling base that would become central to British survival.

  The British Far East Combined Bureau, the FECB, was reading Japanese signals but got key facts wrong. It identified only two carriers in the Japanese force when there were five. It also calculated that C Day was the 1st of April, not the 5th. Somerville, trusting this flawed assessment, sailed on the 30th of March to a patrol area 100 nautical miles south of Ceylon, expecting an attack that didn't come. When the Japanese failed to appear on the 1st and the 2nd of April, Somerville concluded that the intelligence about Operation C had been entirely wrong. He detached his heavy cruisers Cornwall and Dorsetshire to resume their separate duties, and sent Hermes to Trincomalee. The air defences stood down.

  Japanese intelligence had its own failures. Their estimate of air strength on Ceylon was too high, yet they had no idea that Port T existed. The submarines sent to watch the fleet saw little and missed the opportunity to track Somerville's movements. On the afternoon of the 4th of April, the Japanese cancelled a planned floatplane reconnaissance of Colombo harbour, then intercepted a British radio signal that told them the element of surprise was already lost.

• 4. The Warning and the Sinking

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  At about 16:00 on the 4th of April, a PBY Catalina flying boat designated AJ155/QL-A, from 413 Squadron of the Royal Canadian Air Force and flown by Squadron Leader Leonard Birchall, spotted the Japanese Southern Force 360 miles south-east of Ceylon. Birchall transmitted the sighting before his aircraft was shot down. It was the warning that changed the course of the raid.

  Somerville ordered Force A east toward the Japanese. The air defences went back on full alert at 04:00 on the 5th of April. Cornwall and Dorsetshire, which had only just reached Colombo, were sent back toward Force A. The problem was timing: Cornwall was heading for Colombo to resume its refit, Dorsetshire to escort a troop convoy. An aircraft from the cruiser Tone spotted the two ships at 10:00 on the 5th of April, reported them steaming south-west at 24 knots, and began shadowing. They had no way to drive the aircraft off.

  Nagumo reacted immediately. He increased speed from 24 to 28 knots. He ordered Carrier Division 5 to rearm with torpedoes for a follow-up strike, but the rearming took too long. Carrier Division 2 stepped in: Soryu and Hiryu began launching dive-bombers at 11:45. Radar on Force A detected the attack at 13:44, placing the aircraft 34 nautical miles to the north-east. By 14:00, Cornwall and Dorsetshire were sunk with the loss of 424 men. The Japanese aircraft that shadowed the cruisers flew back to Tone without searching further. Had it continued another 50 nautical miles along the cruisers' course, it would have found Force A directly. In the afternoon, 1,122 survivors were rescued from the water.

• 5. Attack on Colombo

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  Shortly after 06:00 on the 5th of April, 91 Japanese bombers and 36 fighters began taking off for the attack on Colombo. British early warning failed to detect the incoming aircraft; pilots had to scramble when the first Japanese aircraft appeared over them at 07:45. The scramble was uncoordinated enough that the defence of Ratmalana airfield left the harbour itself almost unprotected.

  In the harbour an armed merchant cruiser, a Norwegian tanker, and an old destroyer were sunk. Three other ships were damaged. The port itself was struck but not put out of action. At Ratmalana, Hurricane and Fulmar fighters were caught while still taxiing and taking off. Twenty of the 41 British fighters that managed to get airborne were shot down. The six Swordfish of 788 Naval Air Squadron, which had flown from China Bay specifically to be ready for an attack on the Japanese force, arrived overhead just as the raid was ending and were immediately shot down by Japanese fighters. Japan lost seven aircraft over Colombo.

  For Somerville, the scale of the Colombo raid was the first concrete evidence that the Japanese force was far larger than the two-carrier estimate he had been given. He continued steaming toward the enemy at 18 knots. That evening, conflicting intelligence reports made it impossible to determine exactly where the Japanese carriers were. FECB decrypted a Japanese message giving Nagumo's planned movements for the 6th of April, but the transmission was garbled. Somerville ordered his carriers to prepare torpedo-bombers for a night attack, then declined to launch it on the basis of incomplete information.

• 6. Trincomalee and the Loss of Hermes

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  The attack on Trincomalee on the 9th of April followed a pattern by then familiar. A Catalina from 413 Squadron RCAF, setting out from Koggala at 02:56, spotted the Japanese force about 205 nautical miles east of Trincomalee between 07:08 and 07:16. Zeros shot it down before a full sighting report could be transmitted. It was the third Catalina lost since the 4th of April.

  The radar station AMES 272 at Elizabeth Point detected the incoming strike at 07:06, with 91 Kate torpedo-bombers armed with 800-kilogram bombs, escorted by 41 Zeros. Seventeen Hurricanes and six Fulmars scrambled in time. A section of three Hurricanes already on dawn patrol intercepted Zeros 30 nautical miles out to sea and shot down three for the loss of one Hurricane. The China Bay airfield and the port were severely bombed, the monitor Erebus was damaged, and a merchant ship carrying aircraft and ammunition caught fire. Eight Hurricanes and a Fulmar were shot down; Japan lost three Zeros and a Kate.

  Hermes and the Australian destroyer Vampire had been ordered south along the coast and were 65 nautical miles away when Trincomalee was struck. At 09:00 they reversed course. Shortly after the attack on Trincomalee ended, a reconnaissance aircraft found them. Eighty Aichi D3A Val bombers held in reserve on the Japanese carriers attacked at 10:35. Hermes was hit by over forty 500-pound bombs and sank off Batticaloa with the loss of 307 men. Vampire was bombed and sank with eight killed. A nearby hospital ship was not attacked and rescued 595 survivors. The corvette Hollyhock was sunk by aircraft from Soryu with the loss of 53 men. British Fulmars arrived from Trincomalee too late to intervene, though they shot down four Vals for the loss of two Fulmars.

  Nine un-escorted Blenheims from 11 Squadron attacked Nagumo's carriers at around 10:25, achieving surprise by evading the combat air patrol. The bombs fell close to Hiryu but scored no hits. Four Blenheims were shot down on the return. It was the first time a Japanese carrier force had faced a concerted air attack.

• 7. Malay Force and the Bay of Bengal

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  While Nagumo's main strike group was battering Ceylon, a separate Japanese force was methodically destroying merchant shipping in the Bay of Bengal. Malay Force, commanded by Vice Admiral Jisaburo Ozawa, comprised a light aircraft carrier, six cruisers, a light cruiser, and four destroyers. It departed from Mergui on the 1st of April.

  On the 5th of April, at 16 degrees north, 88 degrees east, Ozawa's force divided into Northern, Central, and Southern groups. Aircraft from Ryujo bombed the coastal towns of Cocanada and Vizagapatam a day later, causing minor damage but triggering a mass exodus from both places. The Eastern Fleet was far to the south dealing with Operation C, and the British had virtually nothing in the Bay to protect merchant shipping. In three days, Malay Force sank 20 merchant ships and damaged three more, totalling over a hundred thousand gross register tons.

  The chaos caused by both operations allowed a Japanese convoy carrying troops and equipment to slip into Rangoon undetected. Meanwhile, Japanese submarines operating off India's west coast sank individual ships across a wide arc. One submarine sank the British ship Fultala on the 8th of April, 180 nautical miles west of Colombo. Another sank the US freighter Washingtonian near the Maldives on the 6th of April. After the operation concluded, the six submarines of the 2nd Submarine Squadron were assessed as having produced disappointing results given the density of shipping in the region. Japanese commanders concluded afterward that dispersing the submarines had been a mistake and that concentrating them off Colombo would have been more effective.

• 8. Aftermath and Missed Chances

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  Nagumo ordered the fleet east at 13:25 on the 9th of April. By 19:30 the fleet had changed course to the north-east for the Andaman Islands. During the entire raid, the 1st Air Fleet lost 17 aircraft: ten Vals, six Zeros, and a Kate. Thirty-one men were killed and two were severely wounded. Nagumo sent signals to the Combined Fleet claiming a 77.6 per cent success rate for the dive-bombers. One Japanese pilot described the sinking of the British ships as easier than bombing a target ship.

  The British counted losses of 1,028 personnel, seven naval vessels, and 29 merchant ships. Japan's failure to locate and destroy the Eastern Fleet was the central strategic shortcoming of the raid. Writing in 2017, Andrew Boyd argued that Somerville had underestimated the risks he was running at least up to dusk on the 5th of April. Boyd described him as drawing over-optimistic conclusions from flawed intelligence, grossly underestimating Japanese air strength, and sailing against orders from the chiefs of staff. Yet careful positioning, Japanese errors, and the accidental protection provided by refuelling at Port T rather than Ceylon on the 2nd of April kept the Eastern Fleet alive.

  Boyd called Nagumo rigid and unimaginative. The failure to appreciate that Cornwall and Dorsetshire's course, and the later appearance of British carrier aircraft, were connected was a significant analytical failure. Aerial reconnaissance of Nagumo's front and flanks was inadequate throughout. The same absence of radar that allowed the Blenheims to surprise the Japanese carriers would contribute to disaster at the Battle of Midway on the 4th to the 7th of June 1942.

  The Eastern Fleet withdrew to Kilindini in Kenya. On the 18th of April it was accorded the highest priority for reinforcement, with most of the carriers from the Home Fleet and Mediterranean Fleet pledged for transfer. British intelligence detected the Japanese carrier force moving east in mid-April and tracked its arrival in the Pacific in mid-May. The invasion scare faded. In early May the Japanese carriers fought the Battle of the Coral Sea, and by June, Midway ended the credible threat of major Japanese naval operations in the Indian Ocean for good.