The outbreak of the war in the Pacific on 7 December 1941 (8 December, west of the International Date Line) is often depicted as a stunning surprise. This was not the case, at least at the highest levels of government. By the evening of 4 December Lord Halifax, the ambassador to the US and a man uniquely in touch with intelligence and decision-making in both Washington and London, had concluded that conflict – at least between Britain and Japan, and probably also involving the US – was imminent. “Everything looks exactly like the Japanese balloon going up in the course of a day or two,” he recorded in his diary, “cyphers being burnt, secret messages in that sense, etc.”


Up the balloon went, some 60 hours later. Just before midnight on 7 December, Tokyo time, the armed forces of Imperial Japan fired the first shots of a vast campaign of conquest in the Pacific. A task force of three fast transport ships, escorted by cruisers and destroyers, arrived off the small port of Kota Bharu in north-east Malaya. A reinforced regiment of Japanese troops fought their way ashore onto beaches east of the town, in the face of artillery and small-arms fire from defending Indian Army battalions.

This invasion of the British empire began fully 90 minutes before another Japanese fleet began the attack on Pearl Harbor, some 6,800 miles across the Pacific Ocean. Kota Bharu was the site of an RAF ‘aerodrome’, and British planes were able to mount counter-strikes. One of the transport ships was put out of commission, and the others withdrew to the north, but not before enough of the landing force had come ashore to establish a firm beachhead. Two hours after the Kota Bharu attack, a larger Japanese force – the better part of a division – began to land 100 miles further north in the Kra Isthmus of neutral Thailand.

Economic resources

The strikes at Kota Bharu, the Kra Isthmus, and Pearl Harbor were components of one of the most broad-ranging military offensives ever planned. The objective was to gain control for Japan of the economic resources of south-east Asia, including the Dutch East Indies and of the British possessions of Malaya, Borneo and Burma. Victory would give the Japanese empire economic self-sufficiency and expel the European powers from east Asia.

What the Japanese called the ‘Southern Operation’ required the capture of the main British military base at Singapore, on the tip of the Malay peninsula. They judged a direct amphibious attack on Singapore or the southern Malayan coast to be too risky. Instead, the main thrust would involve sending several army divisions into neutral Thailand, where strong local resistance wasn’t anticipated.

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From the Kra Isthmus, a land advance – expected to last a couple of months – could be mounted 500 miles down the Malay peninsula towards Singapore. The local Japanese naval commander, however, insisted that the RAF airfield complex at Kota Bharu – in British-defended Malaya – had to be neutralised on the first night of the war, in order to protect his vulnerable transport ships off the Kra Isthmus from air attack.

Britain and the neutral USA were not ignorant of Japanese intentions. They shared vital intelligence and assessments. What’s more, the Americans had in 1941 broken the most important cipher system used by the Japanese Foreign Ministry, and they passed the secret on to the British.

Britain and the neutral USA were not ignorant of Japanese intentions. They shared vital intelligence and assessments

In the last week of November intelligence from consular officials warned both countries about increased Japanese shipping movements down the coast of China, and the build up of forces in Indochina. Shared analysis of Japanese naval radio traffic warned that a ‘Southern Force’ had been created, composed of a large number of cruisers, destroyers, transports and submarines, and intended to operate in the South China Sea. In November, it became evident from the diplomatic decrypts – codenamed Magic – that Tokyo intended some drastic steps in the first days of the following month.

The most likely move by the Japanese was expected to be sending troops into neutral Thailand, which would bring their forces 400 miles nearer Singapore than their bases in Indochina. It was also possible that they might strike directly against Dutch or even British territory.

In any event, the government in Tokyo evidently thought its actions were likely to lead to war with Britain, perhaps supported by the US. Japan had been conducting fitful negotiations in Washington for months, but the Magic decrypts revealed that the Japanese Foreign Ministry had warned its posts overseas that the time for negotiation would end at the beginning of December. Meanwhile it had begun to put emergency communications procedures in place. On 3 December the British learned that the order had gone out to destroy code materials in the London embassy, and on the 4th they learned that the same order had been sent to the Washington embassy. Magic also provided information that the Japanese were asking the German and Italian governments to declare war on the US if Washington supported Britain.

How could the British deal with the threat to south-east Asia? There existed a contingency plan, Operation Matador, for sending ground troops into southern Thailand – violating Thai neutrality – and seizing the ports of the Kra Isthmus before the Japanese could establish a foothold there. London was not, however, willing to take such a step unless it was sure of full-scale military support from the US. And, because of the nature of the American constitution, under which only Congress could declare war, the American president, Franklin D Roosevelt, could never fully guarantee such backing.

The British continued to hesitate even after the evening of 1 December, when President Roosevelt gave Lord Halifax an informal assurance of military help in the event of a direct attack on British or Dutch territory.

At this point the British still did not see an immediate military danger to Singapore. Naval reinforcements – the new battleship Prince of Wales and the battle cruiser Repulse – arrived on 2 December. Rather than being deployed to confront a threat from the north, Repulse was sent off on a visit to northern Australia; had this voyage been completed the big ship would have been removed from Singapore for at least two weeks. Meanwhile, rather than preparing local forces for a defence of Malaya, the admiral in charge, Tom Phillips, flew to the Philippines to discuss long-term plans with American commanders.

British caution prevailed even after the evening of 3 December, when Roosevelt gave Halifax another – secret and unconstitutional – promise that the US would give armed help if Britain became involved in a war over Thailand. This promise was followed by a telegram to the commander in Malaya, Air Marshal Brooke-Popham, to the effect that “His Majesty’s Government have now received an assurance of American armed support” in four contingencies, including a war with Japan sparked by British intervention in Thailand. Brooke-Popham was authorised to launch Operation Matador if he believed Japanese action was imminent.

Brooke-Popham did nothing, because he was still not aware of such imminent action. The Japanese invasion fleet left Hainan Island, off south-east China, on the morning of 4 December. Fatally, the British failed to detect it for more than 48 hours. It was only at midday on 6 December that an Australian scout plane from Kota Bharu spotted a convoy of over 20 large, modern transport ships and numerous warships – including battleships, cruisers, and destroyers – headed west off southern Indochina. The weather was stormy, however, and the British scout planes could not be sure, before night fell, of the convoy’s future course. The Japanese, meanwhile, took care to keep their final destination uncertain. From the convoy’s course at dusk on the 6th it could be taken as headed for southern Cambodia (in French Indochina, where Japan already had troops) or for Bangkok in central Thailand.

Brooke-Popham did not interpret the convoy as a direct move against the Kra Isthmus. The Japanese might even be trying to trick him into violating Thai neutrality first, giving Tokyo a justification for war. Based on the direction that the Japanese ships were heading (north-west) when contact was lost, Brooke-Popham guessed that they were making for an anchorage in Cambodia. In any event, London had given him authority to send troops into Thailand, not to attack Japanese ships at sea. He also lacked long-range aircraft and ships able to carry out such attacks.

The daylight hours of the following day, 7 December, were confused. The morning began with Japanese fighters shooting down an RAF ‘Catalina’ long-range flying boat that was attempting to relocate the Japanese convoy, before the doomed crew were able to report the attack.

At midday on Sunday, aircraft from Kota Bharu sighted Japanese transports, but there was still neither the authority nor the capability for air strikes in these hours when the Japanese vessels were most exposed to attack. By 10.30am the invasion ships had fanned out for the landings at Kota Bharu and the Kra Isthmus. At about midnight on 7–8 December, they had reached their destinations unscathed.

Hostile intent

The Japanese attack on Thailand and the British possessions in south-east Asia on 8 December was important for two reasons. First of all, the remarkable intelligence warnings of hostile intent that both the British and Americans received were assumed to apply to Thailand and Malaya, rather than Hawaii. To quote the findings of the Pearl Harbor inquiry conducted by the US Congress in 1946: “Just about everybody was blinded or rendered myopic by what seemed to be the self-evident purpose of Japan to attack toward the south – Thailand, Malaysia, the Kra Peninsula [sic], and perhaps the Philippines and Guam.”

The remarkable intelligence warnings of hostile intent were assumed to apply to Thailand and Malaya, rather than Hawaii

Second, and more important, the initial assault on Malaya and Thailand by the ‘Southern Force’ was as successful as the attack on Pearl Harbor. The Japanese succeeded in leapfrogging into their advance bases on the Kra Isthmus without any loss of shipping, or any pre-emptive move by the British ground forces. And by taking Kota Bharu on the first night of the war they prevented British air strikes against the Japanese transport ships amassed off the Kra Isthmus in the days that followed.

When Admiral Phillips belatedly (on the evening of the 8th) sailed north with Prince of Wales and Repulse for a raid against the invasion fleet he did so with fatal disadvantages. The RAF, having lost the use of the Kota Bharu base, could provide him with neither the location of Japanese ships nor defending fighter planes over his task force. Realising his situation Phillips abandoned the dash north during the late afternoon of the 9th, but he was caught off southern Malaya the next morning. A strike by Japanese navy bombers from Indochina sank both his capital ships with heavy loss of life.

Meanwhile the troops that landed in the Kra Isthmus immediately began a drive from Thailand south towards Singapore. On 11–12 December they broke the line of resistance of Indian and British battalions at Jitra in north-western Malaya and precipitated a rapid retreat which did not end until the fall of Singapore on 15 February. The British would not return to south-east Asia until 1945. Their empire had suffered a loss of prestige at the hands of an Asian nation from which it would never recover.

Evan Mawdsley is professor of history at the University of Glasgow and author of December 1941: Twelve Days that Began a World War (Yale University Press, 2011).


This article was first published in the Christmas 2011 issue of BBC History Magazine