The greatest gamble in military history... and why it backfired

PEARL HARBOR WAS PLANNED BY THE JAPANESE AS A KNOCKOUT BLOW AGAINST AMERICA. INSTEAD, IT WOKE A SLEEPING GIANT AND HELPED GUARANTEE ALLIED VICTORY IN THE SECOND WORLD WAR. ROBERT LYMAN REVEALS WHY

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ONCE the shock of the surprise attacks by Japan in December 1941 on the sleepy British, Dutch and British imperial possessions in East Asia and the Pacific had worn off, the challenge was what to do about it.

Japan clearly had to be defeated but this would take time and an unparalleled industrial and global military effort given that, in 1941, the European colonial powers had been entirely unprepared for the onslaught in the Far East.

But in attacking the US at Pearl Harbor on December 7, 1941 branded a "day of infamy" by America's President Franklin D Roosevelt in a speech to Congress the following day the Japanese had made the cardinal error of awakening a sleeping giant. America's industrial capacity and its potential was unmatched.

The Japanese made the mistake of hoping the US would decide that the military defeat they suffered would be enough to persuade them not to enter the war. It was a profoundly foolish gamble and, in fact, had entirely the opposite effect.

Several factors determined how the Western allies would respond to the challenge laid down by the Japanese once their rampage had been halted.

In the first place, President Roosevelt and Winston Churchill had previously agreed that, if Japan joined the war, the primary effort by the Allies would be the defeat of Germany first.

This meant that victory over the Japanese would play second fiddle to removing the Nazi menace in Europe.

Second, China would need to continue to be supported, as Chiang Kai-shek's Kuomintang forces were tying down more than one million Japanese troops in China, who might otherwise be sent to fight in other parts of Asia and the Pacific.

The first task for the Allies therefore was to stop the Japanese offensive. When that was done, they could decide how to proceed.

Once stopped, they would need to roll the Japanese back and, if that in turn was successful, they would then have to decide how the war was to end.