In the early days of World War II, Australia had felt safe in the shadow of its colonial ruler Britain. But Japanese bombing raids in the tropical north and midget submarine attacks in Sydney Harbour in 1942 awakened the country to its vulnerability to invasion and changed its perception of its relations with Asia and the rest of the world.
With Japan marching unhindered over much of Asia and Britain bogged down in fighting in Europe and North Africa, Australia began to look to the United States to guarantee its security.
Singapore, the symbol of British power in the region, had fallen in February and thousands of Australian soldiers had become prisoners of war.
The Japanese had also taken control of Hong Kong, the Malaya peninsula, Indonesia and parts of Australian-administered Papua New Guinea to the immediate north.
Then on February 19, 1942 more than 243 people were killed when Japanese bombers attacked the northern city of Darwin. About 20 military aircraft were destroyed and eight ships sunk.
Whether Japan ever seriously wanted to invade Australia remains a matter of dispute but the threat was enough to prompt thousands to abandon their homes in the country's north and city-siders as far south as Melbourne to build make-shift bomb shelters in their gardens.
Bob Howard, professor of international relations at Sydney University and brother of Prime Minister John Howard, says it was after these raids that Canberra faced the fact it could no longer rely on Britain for assistance.
"The early months of 1942 were a disaster as far as Australia was concerned. Obviously we had to think 'Who is going to save us?'" Howard says.
"Up until then it had been felt, unconsciously or consciously, that it would be the British.
"(But) Britain was involved in a fight for life, as it were, in Europe. It must have looked particularly grim for Australia in terms of getting assistance from Britain."
America appeared to offer the only hope to an Australian government experiencing difficulties extracting thousands of its own soldiers from battlefields in Europe and the Middle East.
"It didn't go unnoticed in Australia that the Americans were going to be actively deployed in this region and that America was the rising giant," says Howard.
Shortly after Labour prime minister John Curtin took office in October 1941, he spoke bluntly of Australia's position and called for US assistance.
"Without any inhibitions of any kind, I make it quite clear that Australia looks to America free of any pangs as to our traditional links or kinship with the United Kingdom," he wrote in a New Year message.
Curtin knew the feeling in London was that "Australia can go and Britain can still hold on." He was determined that this should not happen.
At his insistence, the commander of Allied forces in the Pacific, General Douglas MacArthur, moved his headquarters to Brisbane in early 1943.
Japanese aircraft continued to bomb northern Australia and submarines travelled as far south as Sydney Harbour where they attacked ships and shelled the eastern suburbs. But the threat of invasion receded as the Allies won battles in the Coral Sea, at Midway and in Papua New Guinea.
Following the war, Australia pushed for a formal alliance with a wary Washington and was eventually rewarded in the 1950s with its most prized treaty, ANZUS (Australia New Zealand United States) which obliges the three countries to defend each other.
"Ideally, Australians would have loved an arrangement that involved Britain but Britain was not going to get involved out here," says Howard.
Australia has followed the United States into each of its major conflicts since - Korea, Vietnam, the Gulf War, Afghanistan and Iraq - but despite the alliance, Australians still harbour fears of an Asian invasion.
The bombing of Darwin "sensitised Australia to its vulnerability," says Bill Tow, professor of international security at the Australian National University's department of international relations. But he acknowledges that the fear of invasion has receded since then, mainly because "Australia increasingly relates to Asia as an economic problem rather than a strategic problem."
Professor Hugh White, head of the strategic and defence studies centre at the Australian National University, says Australia has "a kind of deep-seated anxiety" about its hold on the continent.
"Because the continent seems very big and we seem very few and our neighbours very numerous," he says.
"We live on the edge of a very complex and uncertain region. The possibility of interstate wars is not high but it's not so low as to be negligible. We live in a region in which major conflict is far from impossible." According to media mogul Rupert Murdoch, the US-Australian alliance has been cemented due to the threat of Islamic militancy.
At the time Howard took office in 1996, Murdoch said, relations between the United States and Australia were at their lowest level since the Battle of the Coral Sea in early 1942 and it seemed the countries might drift further apart.
"Then came 9/11 and Bali and Madrid and London. Terror became the great threat to us all," Murdoch told a US Chamber of Commerce dinner during a visit by Howard to Washington last month.