In April 1942, the Japanese launched a major raid into the Indian Ocean with the aim of destroying the Royal Navy’s (RN) Eastern Fleet. The vehicle of this intended destruction was the Imperial Japanese Navy’s (IJN) Striking Force, the same carrier task force that had ravaged Pearl Harbor and other Allied targets since the start of the war. Though the RN had gone to great lengths to reinforce the Eastern Fleet – by April it was the largest fleet yet assembled in the war with three carriers and five battleships – it was vastly inferior to the IJN’s carrier force. The Japanese used five of the six Pearl Harbor carriers and all four Kongo-class battleships for the Indian Ocean raid.

Indian Ocean operations in April 1942 can be quickly summarized. On 5 April, Japanese aircraft struck Colombo on Ceylon (now Sri Lanka). Their assumption that the Eastern Fleet would be caught in port proved false and the strike was minimally effective. However, that same day the Japanese detected two RN heavy cruisers fleeing from Colombo and sank them with an expert dive-bombing performance.

In the least understood part of the engagement, Vice Admiral James Somerville, commander of the Eastern Fleet, attempted to engage the Japanese with night torpedo attacks with his vastly inferior carrier force. This was a high-risk tactic that ultimately proved unsuccessful. At one point, the two fleets were about 100nm apart but neither had full awareness of the other. Somerville and the Eastern Fleet only survived because of the utter incompetence of the Japanese. 

On 9 April, the Japanese launched a large air strike on Trincomalee on Ceylon. This raid was less successful than the Colombo raid just days earlier. But again, the British ineptly dispersed the Eastern Fleet and the Japanese discovered the carrier Hermes and other smaller ships fleeing the port. Again, Japanese dive-bombers quickly sunk Hermes and several other ships in the area. 

Overall, the Indian Ocean was indecisive. The Eastern Fleet and the Striking Force never met in a full-scale engagement. This was one of the great ‘what ifs’ of the war. What were the chances of such an engagement actually occurring? What would have happened if it did occur? What would have been its impact? Read the book to find out. 

Even in a battle that never occurred, it is revealing to examine the performance of the two forces and their commanders. The Striking Force was commanded by Vice Admiral Nagumo Chuichi. He and his staff performed miserably in April 1942. The assumption that they would catch the Eastern Fleet in port and ‘Pearl Harbor’ it proved woefully inaccurate, as was the usual Japanese assumption that they would gain tactical and operational surprise. The blunders of Somerville gave Nagumo the opportunity to accomplish his mission of destroying the Eastern Fleet, but Nagumo lacked the mental agility and flexibility to seize the chance. Japanese operations were marked by pathetic search operations, poor target prioritization in the attacks on Colombo and Trincomalee and poor fleet air defense doctrine. Nevertheless, when the Japanese did find worthwhile naval targets, their attacks were deadly. 

As bad as Nagumo’s performance was, Somerville’s was arguably worse. As commander of the much weaker force, he had little room for error. In spite of his clear orders to preserve the Eastern Fleet and avoid massive damage to British fortunes should it be destroyed, Somerville committed a series of errors that exposed his force to potential destruction. His poor use of intelligence and his creation of a poorly thought out set of assumptions led to his flawed positioning of the Eastern Fleet between 31 March and 2 April in anticipation of a Japanese attack. Had the Japanese begun their raid during this time (as they originally planned), it is almost certain that disaster would have befallen the Eastern Fleet. Another potential disaster could have resulted from Somerville’s decision to rush towards the east from the ‘secret’ base at Addu Atoll after he learned of the Japanese attack on Colombo on 5 April. This was a reckless move without knowing the strength of the Japanese force. Somerville’s plan of staying beyond the range of Japanese air searches during the day and then closing the distance at night almost came to fruition on 5 April. The Eastern Fleet survived April 1942 due to sheer luck, and in spite of Somerville’s determination to expose it to the maximum amount of risk possible without verging into recklessness.

Perhaps the most neglected part of the Indian Ocean Raid was how it foreshadowed the outcome of the Battle of Midway fought in June. The Indian Ocean Raid was a virtual dress rehearsal for it, and many direct comparisons can be made between the two operations. Without giving away too much of the detailed comparison made in the book, these included poor Japanese operational planning, excellent Allied operational intelligence, excellent Allied long-range air reconnaissance, the failures of the IJN’s submarine force, incredibly poor Japanese search operations, poor Japanese aviator ship recognition skills, uncertain Japanese responses to the sudden appearance of Allied naval forces and the associated problems of rearming strike aircraft, the problems with neutralizing Allied bases and the Striking Force’s major problem with air defense.

The weakness of the Eastern Fleet and of British offensive air power on Ceylon meant the Striking Force did not pay for its operational blunders and doctrinal shortcomings in April. Against a peer force like the US Navy at Midway, such weaknesses resulted in total disaster. The Indian Ocean Raid may not have proved to be a decisive event in itself, but it did foreshadow the destruction of the Striking Force and a dramatic change in the fortunes of war in the Pacific.

If you enjoyed today's blog post you can find out more in Japan’s Indian Ocean Raid 1942: The Allies' Lowest Ebb