Similar expressions of solidarity were seen throughout the world.
The outpouring of grief in Ireland was particularly intense.
Long lines of people gathered outside the US Embassy in Dublin to express condolences. Their presence paid eloquent testimony to the almost familial relationship between Ireland and the United States.
On this day, US Independence Day, less than three years later, such a straightforward expression of affinity with America would be unthinkable. The protests that accompanied President Bush's recent visit were the latest display of Irish distaste for US policy.
The vicissitudes of Irish public opinion do not keep anyone in the White House or the Pentagon awake at night. But many Irish-Americans listen to the ever-growing chorus of criticism of the US with dismay.
Where once communication between people in Ireland and Irish-Americans was characterised by mutual understanding, now it seems to be soaked in suspicion and enmity.
There is, of course, a danger in over- simplifying this phenomenon.Tens of millions of Americans lay claim to some kind of Irish heritage and it would be ludicrous to suggest that their views are uniform.
The traditional tendency of Irish-Americans to support the Democratic Party has long since dissipated, for example.
Now, Irish-Americans are as likely to be super-patriots, supportive of a robust American foreign policy and a Republican president, as they are to be proponents of the kind of liberalism espoused by Ted Kennedy.
But the general sense is that, while many Irish people are baffled by what they regard as the bombastic and hawkish views of their America kin, an equally high proportion of Irish-Americans are irked by attitudes in Ireland which they perceive to be overly hostile to the US.
Exactly how America is perceived in Ireland remains open to debate, however.
``I don't think there is hostility to America per se,'' one prominent US-based Irish businessman said. ``But people in Ireland have great difficulty with Bush and with what they perceive to be misguided American foreign policy, not just in Iraq but in relation to other things like the Israeli-Palestinian conflict.''
Bill Flynn, chairman of Mutual Of America, was one of the pivotal Irish-American figures in the peace process.
He offers a less forgiving view of Irish attitudes to the US.
``American people of Irish heritage are absolutely taken aback by what they are observing,'' he said. ``We are shocked by the response [of the Irish people].
People say `It's not an anti-American thing, it's an anti-Bush thing'. But they forget that he's our president. He was elected. Some of the things written and said about him have been in very poor taste.''
Flynn, a confirmed Bush supporter who is adamant that the president will be re-elected in November, argues that many criticisms of America are based on ``a lot of ignorance, particularly of foreign policy considerations''.
Stella O'Leary, chairperson of Irish-American Democrats, sees reflexive anti-Americanism and political opposition to the president intermingling in the streams of Irish public opinion.
``I have been amazed sometimes visiting Ireland, having to listen to these diatribes against America, which, among other things, are always far too general,'' she said. ``Somebody will say quite seriously `Nobody in America is properly educated' or something like that.
``There has always been a resentment of America, and sometimes that resentment seems to come from envy. But George Bush has also seemed to confirm some of the worst perceptions people have of America - brashness, ignoring other opinions and so on.''
Among Irish-Americans, especially those who are supportive of the current administration, much of the blame for Irish opposition to Bush is attributed to the media.
The prevailing view is that the Irish media are liberal and operate according to negative assumptions about America in general and conservative, `strong-on-defence' Republican presidents in particular.
Jeff Cleary is the communications director of the National Assembly of Irish-American Republicans. ``What has always interested me about the Irish media is that so much of the reporter's opinion appears in the story,'' he said.
``Here [in America], with a few exceptions, most papers stay away from that. But in Ireland, a lot of the editorial opinions lean to the left and that is reflected in the stories.''
Flynn puts things more trenchantly.
``When I look at the Irish Times and the Irish Independent, and men like Vincent Browne, Robert Fisk and your own Tom McGurk, I'm amazed at the stuff they get away with,'' he said. ``McGurk wrote an article about Ronald Reagan shortly after his death which was the most incredible display of bad taste.''
Though there is strong agreement among many Irish-Americans that the Irish media propagate a hostile view of the US, there is much greater divergence on another hot topic.
It is sometimes suggested that widespread criticism of the US will discourage further American investment in Ireland.
Flynn believes this is a real danger.
``The attitudes in Ireland [towards America] are really changing the whole situation,'' he said. ``There are conversations going on in any number of corporate boardrooms in America at the moment, where they are threatening to pull out of Ireland.
"Someone who I know personally is advising everyone to get out of Ireland because of all this, and he would previously have been very supportive.''
Some scoff at these ideas. A prominent Irish businessman in New York is among the doubters.
``Business people are there to make money,'' he said. ``If I was a shareholder in a company that moved in or out of a country for political reasons, and endangered profits in the process, I'd have serious questions.
"In one way, Bertie [Ahern]'s almost sycophantic attitude to Bush is unnecessary - it's not going to affect business decisions one way or another.''
The cold calculus of business is only part of the story. The real danger is that the current political gulf separating Ireland and America will have more general, long-term effects on the relationship between the two countries.
The enormous benefits that Ireland continues to glean from American engagement, whether in the peace process, in tourism or in industry, would be imperilled if American goodwill towards Ireland began to wane.
O'Leary said she noticed no erosion of Ireland's appeal yet. She said: ``Americans absolutely love the Irish and I see no signs of that changing - the majority of Americans wouldn't even be that aware of the views held in Ireland. And `Ireland' is just like a magic word to them.''
Others are not so sure, however. While Flynn acknowledges the personal warmth which continues to be shown by Irish people towards American visitors, he also believes the political differences are taking their toll.
``I think there is profound disappointment [among Irish-Americans] about what is going on in Ireland,'' he said. ``It is threatening the American public's appreciation of Ireland.
``There was great sympathy and goodwill there [in America], and it came through in everything from fighting for Green Cards on up. But that goodwill is disappearing. The view in America now is becoming `why are we for them when they are against us?'''
Britain has long boasted of enjoying a ``special relationship'' with the US. The same could have been said of Ireland.
There are too many ties for that relationship to be dissolved easily. But it has entered very stormy waters, from which it might take a long time to emerge.
