The royal tribute was too emotional for many
For the thousands of Americans who visit London every year, the traditional Changing of the Guard ceremony at Buckingham Palace is a must-see event.
But on Thursday, the daily spectacle took on a special significance and personal resonance as the Queen's guards played the US national anthem, followed by a two-minute silence.
It was a mark of respect for victims of the atrocities in New York and Washington on Tuesday.
The chilly weather did not deter a crowd of about 35,000 people who arrived in front of the palace to witness the unprecedented event.
Patti Leanna, a tourist from Tennessee, said: "I just had to come to hear our national anthem today - when I heard the news of the attacks I was devastated. I can see absolutely no reason for it."
Sobs
Most of that crowd were Americans, stranded in the UK since flights home were suspended following the terrorist attacks.
Their mood was subdued and emotional. Many hugged companions, cried and leant against each other in the cold.
The bleakness of the atmosphere was broken by the arrival of the guards, with their bright uniforms and the music of the band.
There was a buzz of excitement as people strained to see them as they paraded into the palace courtyard.
But when the first chords of the Stars and Stripes struck up, the grief felt by many in the crowd came to the fore.
Many people sobbed, with their heads down. Others gave the sign of allegiance to the American nation. Most sang the words to the anthem.
The two-minute silence was broken only by muffled sobbing. It was followed by a spontaneous round of applause - for America but also for the United Kingdom.
Neil O'Brien, from New York, said: "It was very touching hear our national anthem. It's nice to know that the British are with us.
"Everyone here has been really kind, particularly in our hotel. And when we heard Tony Blair say the British were standing shoulder-to-shoulder with the US people it was fantastic."
There were also many British people in the crowd who had come to the palace to show their respect and support.
Mrs Cartwright from north London said: "I felt I had to come down today - I have been very moved by this awful event."
Changed
New Yorkers Rickie and Monroe Haas said: "It is indescribable, horrific, in fact there are not any adequate words to talk about this terrible act of violence.
"We watched it on the TV and just couldn't believe it was happening. There is something inhumane about taking a plane full of people to kill others."
There was a general feeling among both the British and Americans that "something had to be done" in response to the attacks.
But most were also tentative about exactly what that response should be, particulary since the perpetrator of the attacks had not been established.
All the Americans were united in their feelings that "nothing would ever be the same again" - and that all they wanted was to get home.
A mother from Philadelphia, in London with her teenage son, said: "We just want to go home. We can't get a plane and all we can do is keep calling our family but even that is hard. We feel violated and changed forever."