Queen Elizabeth II on Tuesday deployed British royalty's grandest pomp for US President Barack Obama, on a state visit meant to prove a "special relationship" remains "essential" in a world of shifting power.
Obama and his wife Michelle got a regal welcome from the queen, who has met every US president but one since the 1950s, as a 41-gun salute boomed out over London and Buckingham Palace choreographed the splendour of a state dinner.
Prince William and his tanned bride Catherine meanwhile added a twist of glamour, meeting the US first couple just after returning from the Seychelles honeymoon that capped their fairytale wedding last month.
Obama's visit, the second stop on a European tour, comes as Britain seeks to prove its staying power despite fading military might and Washington looks to retool its decades-old alliance with Europe as a catalyst for global action.
The meat of the visit, discussions over the uncertain state of NATO's operation in Libya and Obama's efforts to win backing for his bid to coax Tunisia, Egypt and other Arab states towards democracy, was set for Wednesday.
But his first day in London was devoted to ceremony -- with a palace welcome, a pilgrimage to the tomb of the unknown warrior in Westminster Abbey and the swapping of elaborate gifts with the royals.
The queen said at a glittering white tie state dinner that Obama's visit recalled "our shared history, our common language and our strong intellectual and cultural links."
"Your country twice came to the rescue of the free and democratic world when it was facing military disaster," she told Obama, in a reference to the two world wars.
Obama concluded his toast with a quote from Shakespeare's Richard III.
"To her Majesty the Queen, to the vitality of the special relationship between our peoples and in the words of Shakespeare, 'to this blessed plot, this earth, this realm, this England.'"
And breaking free from starchy convention, he drew a regal smile as he told the queen his daughters Malia and Sasha "adored" her.
There was one hiccup when the string orchestra of the Scots Guard began playing the British national anthem before Obama had finished his speech, resulting in a breach in protocol as the president continued to talk over the music.
However, the queen did not appear to be offended and thanked the leader for his "very kind" words.
The Obamas started their day with the royal newlyweds at Buckingham Palace, and Catherine, the new Duchess of Cambridge looked poised and glamorous in a picture released afterwards, showing her chatting with Michelle Obama.
There were also fresh signs of real warmth between the Obamas and the royals, who appeared to bond -- with the queen and First Lady unusually putting their arms around one another -- in their first meeting two years ago.
"There is a genuine, genuine -- and I really mean this -- a genuine warmth between the two families," a palace spokesman said.
White House deputy spokesman Ben Rhodes painted the queen, who has been on the throne for nearly 60 years, as an emblem of continuity for US-Britain ties, from her young adulthood in World War II, through the Cold War, to the present day.
"She is a historic figure who in many days embodies the depth of the ties between our nations," Rhodes said.
Cameron and Obama limbered up for their talks and a press conference on Wednesday with a joint-opinion article in The Times newspaper and vowed to support those risking their lives for reform in the Arab world.
In a riff on the so-called "special relationship" between the US and Britain, Obama and Cameron also heralded a new "essential relationship" between the countries.
Diplomatic and military manoeuvring is heating up over Libya ahead of the G8 summit in France, Obama's next stop on a European tour which began with a journey to his ancestral roots in Ireland and also takes in Poland.
But the 24-hour demands that follow a US president everywhere shadowed the London pomp, as Obama took time out to say he was "heartbroken" at the toll of vicious tornados which ripped across the US midwest, killing 122 people.
On Tuesday, after the formal welcome and lunch, the queen showed the Obamas US-related items from the royal family's archives.
In the traditional exchange of gifts, the royals gave the Obamas a gift of letters to and from US presidents to Queen Victoria in the 19th century.
In return, the president gave the queen and her husband a leather-bound album of memorabilia of a visit made by her parents, King George VI and Queen Elizabeth, to the US in 1939.
In a slice of history, at Westminster Abbey, America's first black president passed beneath a statue of civil rights leader Martin Luther King, installed above the ancient abbey's Great West Door in 1998.
On Wednesday, the president is granted the rare honour of addressing both houses of the British parliament.© ANP/AFP