Every European government expressed its outrage and sorrow at the atrocities in the US. But few countries went as far as Britain.
Immediately after the scale of the attacks on New York and Washington were known, the British Prime Minister, Mr Tony Blair, cancelled all his appointments to chair a meeting of his government's emergency committee. The same group convened twice again yesterday, with full presence of Britain's security services and military chiefs of staff.
An emergency cabinet meeting follows today and an extraordinary session of Parliament is convened for tomorrow. Mr Blair's reaction could not have been very different had Britain itself been attacked. But this is precisely the image which London wishes to convey, in pursuit of long-term foreign policy calculations.
Although the feelings of dismay and horror are genuinely felt throughout Europe, Britain and Ireland were always bound to be in a special position. Both countries have large communities in the US, and almost certainly lost some of their own citizens in the massacre.
Both enjoy a unique relationship with the US which, crucially, includes precisely the question of what is the appropriate response to terrorism. So, in many respects, Dublin and London were always bound to react to this week's events in a particularly strong manner.
Yet Mr Blair's agenda extends much further: he is seeking not only to provide comfort and support for the people of the US, but is aiming at influencing the security debate between Europe and America in the years to come. Because of their exceptionally close connections with the US in sharing intelligence material, security officials in London were quick to predict the implications of the terrorist attacks on America's long-term military planning.
The US will spend months reorganising its intelligence apparatus. Washington will have to reassess its international military commitments, and divert more resources to the defence of its homeland.
Debates about European security arrangements and the problems of the Balkans are now more or less irrelevant, as the White House concentrates on its most immediate task: fighting international terrorism. If not handled correctly, the fallout from this week's bloodshed could lead to a more unilateralist US, a superpower which is both reluctant to continue shouldering the burden of international security and more determined to fight on its own terms against perceived enemies around the world. For Europe, this will represent a major loss; for Britain this will be a calamity.
So Mr Blair has set about trying to influence America's strategic thinking. The strategy involves noisy and very clear expressions of support for the US tragedy; the aim is to persuade Americans that their grief is Europe's grief as well, and the terrorists struck not only against the US, but against the entire democratic world.
It was therefore no coincidence that Mr Blair's pointed reminders yesterday about British citizens who may have died in the atrocity were accompanied by the rejoinder that what has happened in Washington and New York actually struck directly at British interests.
Behind the scenes a much more intricate strategy is developing. British government officials are in constant contact with their US counterparts, trying form joint strategies to tackle the threat.
The calculation is that Washington is bound to take some action; London's hope is that it may be able to influence the shape of this action, and preclude any rash course.
Initial indications suggest the strategy is working. In a remarkable departure, NATO considered yesterday the possibility of invoking a special article in its founding treaty, allowing it to come to the defence of any of its members if it comes under a direct attack.
Historically, this article was seen as providing a US military guarantee for Western Europe during the decades of the Cold War. But the article is being reinterpreted as ensuring Europe's guarantee for US security.
The advantages of adopting this course are immense, as London was quick to realise. For years Washington accused Europe of enjoying an American military umbrella on the cheap, of benefiting from a US security guarantee without paying the bills. It is now the turn of the Europeans to pay some of the bills.
The strategy is not without its risks. The European consensus on supporting the US may quickly crumble once the numbing pain of the tragedy dissipates.
The differences between the US and Europe over the peace process in the Middle East, the sanctions against Iraq and policy over Iran remain as acute as ever.
Although Mr Blair has been good at voicing his support for the US, it is not obvious whether this would extend to joining any US military action. But, at least for the moment, Mr Blair is entitled to feel vindicated. Yet again, he appeared as the most vociferous pro-American in Europe. Yet again he tried to lead the security debate across the Atlantic. And yet again he managed to give the impression that London intuitively understands Washington's concerns.
Security relations are about deeds rather than words. But impressions are important, particularly at such traumatic moments.
Jonathan Eyal is Director of Studies at the Royal United Services Institute in London