The moment the sleeping giant of America FINALLY woke up to wage war on fascism

The attack on Pearl Harbor on the morning of December 7, 1941, was an operational masterstroke but a strategic failure. Visiting the solemn memorial today, among crowds of tourists open-mouthed at the sight of the mangled wreckage of the USS Arizona, sunk at its shallow mooring during the carefully planned and skilfully executed strike, it's hard to understand how the Japanese ever thought they could win a war against America's might.

So why did they launch their attack? The answer lies in Japan's imperial ambitions. The country had been engaged in an imperial adventure in Manchuria since 1931 and in China itself since 1937.

By 1941 the idea of controlling China was existential to Japan. Without China, Japan would not have an empire, and this is what it desired above all else. The problem, however, was that to fuel its war against China's nationalist Kuomintang armies required oil, rubber and steel - none of which Japan could provide itself.

But neither, too, were the European and American colonial powers in Asia prepared to sell their resources to Japan because they knew precisely what they would be used for: a creeping, racial war in China of the sort that had already produced the horrendous Rape of Nanking in 1937, when more than 200,000 civilians were massacred by the Imperial Japanese Army in the city, then China's capital.

During the latter half of 1941, the US knew Japan was preparing for war in the western Pacific and South-East Asia because it had broken the Japanese diplomatic cypher.

But America never had any inkling at any time before about 7.50am on the morning of December 7, 1941, that the plans for a general invasion of the region included a debilitating strike at the temporary home of the Pacific Fleet at Pearl Harbor in Hawaii.

Subsequent attempts to suggest that US president Franklin D Roosevelt - and by extension Winston Churchill - knew of the impending attack yet did nothing in order to facilitate America's entry into the war, have no shred of evidence and serve perhaps to paper over the deficiencies in military planning that enabled the attack to be so effective.

The Japanese government used many codes but the only one that had been mastered by American cryptographers was the diplomatic cipher. JN25b had been partially unravelled by the time Japanese aircraft were making their final dive-bombing and torpedo runs against the Pacific Fleet.

However, every Japanese code was eventually broken - the intelligence gathered making possible the victorious American ambush of the Japanese navy at Midway in 1942 and, later, the shooting down of Japanese admiral and naval commander-in-chief Isoroku Yamamoto during Operation Vengeance in April 1943.

But that was still to come. For Churchill, the entry of the US into the war meant the ultimate outcome - favourable for his country - was now assured. Feeling "the greatest joy" that the attack had arrayed his mother's country on the side of Britain, he later recalled how that night he "went to bed and slept the sleep of the saved and thankful".

Consequently the US, the Netherlands and Great Britain increasingly refused to allow Japan free access to resources.

The Japanese attack on Pearl Harbor was not an isolated military operation, nor merely a lashing out by an out-of-control military but a key component of a much larger plan, at the heart of which was the capture of (mainly) European colonial possessions in South-East Asia.

Pearl Harbor came about because Japan needed to protect the seaward flank of its invasion of South-East Asia from
interference by the US Pacific Fleet, based in Hawaii.

The country's military planners had two choices: allow the fleet to sally out in response to the Japanese invasion and engage it in open battle on the high seas or, preferably, prevent it from sailing at all.

Japan's political ambition was not to go to war with the US - merely to restrict America's military options at a time when Japan was attempting to maximise hers.

Could it have done things differently and thus prevented, as Admiral Yamamoto - the architect of the attack - feared it might, awaken the sleeping American giant?

Japanese planners led by Admiral Isoroku Yamamoto, who masterminded the raid, thought a robust and bloody first strike might persuade an inherently isolationist US not to engage in war at all, especially when ships and military effort generally was at that very moment being concentrated on the Atlantic and the threat to American interests there by German U-boats.

But military necessity dictated that Japan would have to take the risk of war with the US if it wished to achieve its political ambitions in China. There was no other option.

So, the attack on Pearl Harbor can be seen as an attempt by Japan to prevent war with America - not provoke it. But this entailed crazy risk.

So, on Sunday December 7, 1941, at 7.48am the calm of the early morning above Hawaii was shattered by the
unexpected roar of hundreds of incoming aircraft engines.

For residents readying themselves for breakfast, it seemed like an unexpected aerial display to celebrate the weekend.

Then, suddenly, many of the aircraft - there were 182 in total - began falling in unison from the sky, engines screaming as they dived. Slowly, shocked awareness dawned on those watching far below. This was no peaceful display.

Wave after wave of aircraft threw themselves against the US Pacific Fleet at anchor in the shallow waters. The drone of bombers manoeuvring to fire their torpedoes at the eight sleeping battleships moored alongside on Battleship Row on Oahu Island was mixed with the scream of Zero fighters strafing unprotected airfields, shooting up rows of parked aircraft into hellish conflagrations of flame and burning steel. High above, bombers steadily dropped their loads of huge, 800kg, armour-piercing bombs on to the unprotected decks of the ships. What had promised to be another quiet Sunday in paradise was shattered in a matter of terrible moments.

Then, just as suddenly, the wail of falling bombs and the dull whomp of detonating torpedoes were replaced by silence - oily smoke pumping skywards to turn the morning brightness into the darkest of nights.

The billowing clouds were the perfect signal for the second rush of aircraft, day into night. A further 171 aircraft began their bombing and attack runs. More bombs fell, more men died - blown up, burned alive or drowned. Nineteen ships were wrecked or damaged along with 347 aircraft, 188 of which were destroyed. War had come to Hawaii and to America, and had done so with sudden and shocking ferocity.

That morning 3,581 American civilians and servicemen were killed or wounded in the surprise attack that President Franklin D Roosevelt would describe as a "day of infamy" - the shallow waters of Oahu a horrifying mix of blood and oil.

Did Japan really believe it could knock the US out of the war? Even without the benefit of hindsight, calculations were naive.

In the first place it miscalculated the intensity of the anger Americans would feel for the deaths of thousands of their innocent boys. Second, it was entirely uncomprehending of the role brave China played in the popular American mind.

Third, by taking on the US, the Japanese were provoking a country with a war potential that far outstripped their own; the laws of economic and military consequence ruled that Japan - while it might win some short-term, tactical successes - would nevertheless lose the war.

Finally, Japan misunderstood the sea-change in terms of isolationism: America never sought war but, when it arrived, non-interventionism would quickly vanish in exchange for the flaming sword of retribution. The fury that December 7, 1941, evoked demonstrated just how massively Japan had miscalculated. In sowing the wind, she reaped the whirlwind.

Within six months the decisive defeat of the Japanese fleet at the Battle of Midway, when four aircraft carriers were sunk by the US, began the process of destruction Pearl Harbor had unleashed, which reached its inevitable denouement at Hiroshima and Nagasaki in August 1945.

• Dr Robert Lyman is author of A War of Empires: Japan, India, Burma & Britain: 1941-45 (Bloomsbury, £16.99)