Within three days of the terror strikes, Howard had invoked for the first time section IV of Anzus, under which an attack on one member of the alliance is regarded as a threat to the safety of the others.
In this event, each party agreed to act to meet the common danger in accordance with its constitutional processes.
"At no stage should any Australian regard [the World Trade Center and Pentagon attacks] as something that is just confined to the US," Howard said. "It is an attack on the way of life we hold dear in common with the Americans. It does require the invocation of Anzus."
Even in the days when New Zealand was a member of the alliance, it is doubtful if such a declaration would have been made with such speed and vigour in Wellington, where there have always been reservations over the degree to which the nation should commit itself to American actions.
In the political and military alienation that followed the banning of nuclear warships in New Zealand's ports, there is no Anzus for Wellington to invoke and far greater cause for caution and for a broadly recognised international legitimacy for the creation of coalition expeditionary forces.
Although Foreign Affairs Minister Phil Goff immediately offered whatever practical help may be sought by the US, Prime Minister Helen Clark was still equivocating on the possible commitment of military assistance two days after Howard had invoked Anzus, extended the deployment of the frigate HMAS Anzac in the Gulf and put his forces on standby.
Although Clark subsequently raised the possibility of New Zealand SAS troops joining US-led forces on whatever battlefield may emerge, there is obvious relief that Washington is taking its time and using great caution in determining its response.
For both countries, any contribution to US retaliation will be token and intended as a political declaration of support. Even Australia's larger forces would vanish with barely a ripple into the vast American pool.
But Canberra believes symbolism is as important as muscle. The invocation of Anzus, said Howard, had a symbolic resonance "but it also means something in substance, and it does mean that if action is taken then we will naturally consider any requests for help from the Americans".
So far, that offer has resulted in the extension of HMAS Anzac's deployment in the Gulf, as part of the blockade of Iraq, from September 16 to October 3, with the possibility of it being replaced by other ships.
Australian troops already on exchange duty with US and British forces will serve with their units in any action against terrorist bases, and speculation is high that the Australian SAS could take part.
The powerful joint US-Australia spy base at Pine Gap, near Alice Springs, will also be used to sift through masses of electronic transmissions in the hope of finding a trail to bin Laden.
The New Zealand facility at Waihopai is also likely to be helping sift the ether for Washington, because of its tight links to similar Australian installations, Wellington's membership of the US-British-Australian information network and Helen Clark's offer of intelligence support.
In terms of relative capabilities, New Zealand's participation in America's anti-terrorism coalition may not at this stage, at least, be far behind Australia's.
But where there is vast difference is Australia's public willingness - even eagerness - to leap behind America with anything at its disposal. Suggestions have ranged from the lunatic fringe's call for conscription to serious discussion on the possible use of the RAAF's F-111 strategic bombers.
"You are either a close ally of the US or you are not, and you can't be a fair-weather friend, you can't cherrypick our most important alliance," Howard said.
There is concern that Australia could be led into a conflagration far beyond the intended meting out of justice to the organisations responsible for the carnage in New York and Washington.
The internet is buzzing with opposition to the Australian position and fears of an anti-Muslim backlash.
The Sydney Morning Herald said Australian self-interest was involved, and claimed most would support the decision to commit the nation to an appropriate role in a US-led campaign against terrorism.
As Howard said, the World Trade Center atrocity was as much an attack on the values of Australia as those of the US. Dozens of Australians were among the thousands killed.
But the newspaper warned as well that the Government must also reserve its right to disagree and even opt out if it believes the US is planning actions likely to be needlessly risky, poorly targeted or to involve unacceptable civilian casualties.
Australia has always been a more enthusiastic ally of the US - although New Zealand has also fought with America in every major conflict since the First World War - because of its deep sense of geographic insecurity.
The bombing of Darwin and the Japanese invasion of New Guinea hammered that home and gave substance to the 1941 declaration of Labor Prime Minister John Curtin that "Australia looks to America, free of any pangs as to our traditional links or kinship with Britain".
Australia was a far more forceful advocate of Anzus as a bulwark against communism when it was first proposed in the grim, early days of the Cold War, when Korea was in flames and the first warnings of 25 years of Southeast Asian conflict were emerging in Malaya and Indonesia.
New Zealand's reluctance had a number of origins - among them the concern that a US commitment might conflict with earlier undertakings to fight with Britain in the Middle East in any new war with the Soviet Union.
This divergence of concern, and of successive strategic perceptions, has underlain and bedevilled the transtasman defence relationship for decades, magnified by the politics of populations which share equally different views of security.
Most New Zealanders continue to support the nuclear-free policy and accept the consequent loss of military kinship with the US; most Australians believe the US stands ever ready to come to their aid, and are willing to pay the price for this.
The fact that Anzus does not guarantee protection - as shown by the US refusal to intervene on Australia's behalf during the Indonesian confrontation of the 1960s - has always been lost in the rhetoric.
Support for the US is bipartisan, and by far the most important element of Australia's foreign and defence policy, reiterated in last year's defence white paper and in repeated policy statements by Government and Opposition leaders.
In 1990, Australia was the first country to offer support for the US coalition against Iraq's invasion of Kuwait, sending warships and navy divers. New Zealand's commitment was a less warlike, but dangerous and politically important, deployment of C-130 Hercules and Army medics.
Eight years later both countries were quick to send military units when war again threatened the Gulf.
But unlike New Zealand, Australia supports the US beyond United Nations-sanctioned coalitions or internationally approved operations such as the present campaign against terrorism.
Australia was one of the few to endorse American brinkmanship with China during the crisis over missile testing and war games in the Taiwan Strait, and continues to be almost alone in offering support for the controversial missile shield.
As well as potential support in any attack on Australia, Canberra regards its alliance with the US as a means of continuing to enmesh American interests with the region, and of ensuring that its military can do the jobs demanded of it.
"Australia's ability to shape the regional security environment is substantially dependent on our defence relationship with the US," Foreign Minister Alexander Downer told a recent Anzus conference.
Labor Leader Kim Beazley added: "Anzus is the foundation of our strategic relationship and to my way of thought is one of our great national assets as we enter the 21st century."
The shoulder-to-shoulder rhetoric of Australian support for the anti-terrorism coalition also has a large degree of self-interest developed much closer to home.
The nation has already suffered a number of terrorist attacks aimed at a variety of international targets, and terrorism experts have warned that a number of groups are operating within the country. And a group of Indonesian Muslim leaders have called for a holy war if Afghanistan is attacked.
This has already uncovered serious social implications at home.
Muslim children have been attacked in Melbourne, mosques have been bombed and burned, and racial vilification has again become a painful and dangerous part of life for Australia's Islamic population.
This threatens to further inflame the passions aroused by the refusal to allow Afghan asylum-seekers to land from the Norwegian freighter MV Tampa, and UN warnings that Australia may need to take many more refugees if war in central Asia pushes out a greater wave.
Despite this, and Howard's warnings that Australian troops could be killed in a campaign against terrorists, his unapologetic support for the US has struck a powerful chord in the Australian psyche.
His standing in opinion polls has soared, pushing his Government from almost certain defeat to what at this stage of swelling nationalism appears to be an unassailable lead in the run-up to the election.
In Australia, it is still all the way with the USA.
16 days on ... How the NZ Government reacted to the terrorist attacks
SEPTEMBER 11
With Prime Minister Helen Clark still overseas, Foreign Affairs Minister Phil Goff says NZ will help in any way practical. "We stand alongside the people of the US to do whatever we can to help them in the face of this incredible tragedy."
SEPTEMBER 16
Clark offers to share intelligence but backs off from sending troops or logistical support to any US-led military attack. "We have said 'count us in' for an international effort to combat terrorism. Beyond that, there have been no requests of any sort." She hints at more money for intelligence agencies.
SEPTEMBER 17
Clark extends her offer by suggesting our SAS troops could also be used.
SEPTEMBER 18
The Government orders a review of NZ's ability to counter terrorists after officials assess a "modest" increase in the threat to security. Security is stepped up at airports and extra baggage screening introduced.
SEPTEMBER 19
National and Act accuse the Government of being lukewarm. "We can be supportive without being sycophantic - and the Government cannot tell the difference," says National deputy leader Bill English.
SEPTEMBER 20
As President Bush prepares to deliver an ultimatum to the Taleban to give up bin Laden, Clark says: "The good news is the US is taking a long time to think about this."
SEPTEMBER 27
A Business Herald-Auckland Chamber of Commerce poll finds 20 per cent of Auckland businesses rate the Government's handling of the terrorist crisis as very bad.
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America
