operations -- protecting each other's backs in war -- and that "absolute openness, close co-operation" characterises the transatlantic military alliance.
President George W Bush heralded Prime Minister Tony Blair as "a man of his word...a man of courage...a man of vision" when the British leader visited Washington last week.
Yet Britain and the United States are waging different wars on the ground -- Britons mop up in the south while Americans charge on to Baghdad -- and envision conflicting post-war scenarios that reflect their leaders' diverging politics.
"Clear differences are emerging between the Americans and the British in the way they are conducting the war," said Colonel Christopher Langton of the International Institute for Strategic Studies think-tank.
US forces have drawn rebuke for killing Iraqi civilians and British troops in a series of shooting incidents.
British troops, by contrast, have drawn on their experience of Northern Ireland's conflict to navigate their way more quietly around the Iraqi battlefield, even swapping helmets for berets to present a more benign face.
"The British have been able to fall back on their experience so easily. The Americans have not," said Langton.
Take this week's checkpoint killings of eight Iraqi civilians, when edgy US troops opened fire in incidents that will set back efforts to win over locals or sceptics back home.
Many believe British troops are less trigger-happy under threat, hardened by their training in Northern Ireland.
"We don't get fazed by urban warfare because we've had 30 years in Belfast -- soldiers walking the streets waiting to get shot in the back is what we do," a defence source said.
"It's in our psyche."
A British soldier injured in a "friendly fire" accident angrily branded the US pilot a "cowboy" with no regard for human life for his quick-fire decision to shoot.
Nor are British officials any more at ease with the US desire for swift victory, whatever the cost in Iraqi life.
A senior US official said this week that the United States was prepared to pay a "very high price" to capture Baghdad.
"If that means there will be a lot of casualties, then there will be a lot of casualties," said the official, in the sort of macho comment that makes military men pale in London.
Minimising casualties is a top British priority, not an optional extra, said the defence source, citing public ambivalence to the war.
"It will be politically unacceptable to go in and flatten Baghdad. That is not the way we can do business and the British would have a problem with that," the source said.
What sort of peace?
Nor is the diplomatic axis all unity.
Britain wants the United Nations to run post-war Iraq while the United States, livid with the UN's failure to endorse its war, wants to control the reconstruction.
"For the UK, a post-war Iraq will be in a UN setting. The Americans would prefer a US administration running all the major ministries. They would stay until the oil runs out," said Paul Rogers, professor of peace studies at Bradford University.
"The US are being seen less as liberators and more as conquerors. The UK is still more serious on 'hearts and minds'."
London and Washington have drafted very different post-war scripts for Iraq's neighbours, with Britain pushing hardest for progress on Middle East peace.
Blair has made strenuous efforts to develop ties with Syrian President Bashar al-Assad while his foreign secretary, Jack Straw, has visited Tehran three times.
Yet Bush has branded Iran part of his "axis of evil" and Syria and Iran have come under attack from his acid-tongued defence chief, Donald Rumsfeld. Bush has promised a "roadmap" for a lasting settlement between Israelis and Palestinians but attacks on top regional powers will do nothing to advance peace.
"We would certainly have chosen different language," said one British official, embodying the very reserve that many see as lacking in Bush's Washington.