American National Anthem played at Buckingham Palace after 9/11
For those interested, this is the only time in it's 200 year history that another country's national anthem has been played outside Buckingham Palace, apart from during state visits. Her Majesty the Queen personally authorized the Coldstream Guards to break protocol and play this, to give some comfort to Americans stranded in London due to airport closures. It is literally the highest gesture of solidarity Britain could show to another country.