About 4 o'clock this afternoon the most immense passenger ship the world has seen - double the weight of the QE2 and three times the weight of Titanic - will glide from the harbour at Saint-Nazaire on the French Atlantic coast.
An orchestra will play God Save the Queen and the Marseillaise; French fighter planes will fly overhead and up to 100,000 people are expected to line the harbour mouth, carrying lanterns and torches.
They will salute, with mingled sadness and joy, the departure from her birthplace of the Queen Mary 2 - the longest, tallest, widest and heaviest passenger ship ever constructed; the first ocean liner to be built for 34 years and maybe the last.
The QM2, touched by tragedy even before she was completed, represents a vast, ocean-going gamble for Cunard, the British shipping line which ordered her three years ago. She is not just a floating hotel - with five swimming pools, 14 restaurants, 24 massage parlours and an art gallery - she is a true, ocean liner in the Cunard tradition.
The ship will be capable of crossing the Atlantic in six days. Her engines can generate enough power to light a city of 300,000 people.
But many voices in the shipping and cruise industry have wondered aloud whether there is an economic future for such a luxuriously appointed, speedy, highly engineered and technically advanced ship.
They suggest that the real salvation for a cruise market - holed below the water line by the terrorist attacks in the United States in September 2001 - is for larger, slower, floating holiday resorts which can meander around the South Seas, offering a wider range of cheap to expensive cruises.
There are good reasons, they say, why no one has bothered to build a real ocean liner since 1969 (Cunard's QE2 was the last).
Cunard insists that the QM2, designed internally to recall the great Art Nouveau days of the ocean liners in the first half of the 20th century, will be able to perform both roles.
She will be a true liner for those who want to travel to the US in superb, retro style; she will also be a leisurely cruise ship. The ship's first year of cruising and Atlantic crossings, starting next month with a trip to Fort Lauderdale and the Caribbean, is already almost fully booked.
More exuberant celebrations planned by the town and shipyard at Saint-Nazaire to say farewell to the Queen have been cancelled since last month when 15 local people died after a gangway which linked the liner to the harbour-side collapsed.
There have been suggestions that this somehow makes the QM2 a cursed ship even before it joins the Cunard fleet; even before it is named by the Queen at Southampton, its home port, on 12 January.
In truth, the accident had nothing to do with the quality of the workmanship on the ship itself. The makeshift gangway had been built by a contractor to a weaker specification than normal, for reasons that remain unclear. More than 50 people were allowed to stand on it at the same time, as they queued for an open day at the ship.
Saint-Nazaire, preferred by Cunard to Harland and Wolff in Belfast, is immensely proud of its achievement in building such a gargantuan and advanced ship in two years within the £500m budget. But even in Saint-Nazaire, the QM2 has come to be known as "Bloody Mary" or the "Red Queen".
The disaster has been taken as an ill omen - if not for the ship then for the shipyard. The yard, Les Chantiers de L'Atlantique has received no new orders for cruise ships for almost three years. When the QM2 departs, it will leave behind an almost empty shipyard, with just one smaller cruise ship and a methane tanker nearing completion.
The size of the QM2 takes the breath away. She is 345 metres long - as long as the Eiffel Tower is tall, and 50 metres longer than the QE2. She is 41 metres broad, double the width of the Titanic. She is 74 metres high - 62 metres above the water line, the equivalent of a building 23 storeys high.
In terms of weight - 150,000 tonnes - she is more than double the size of the QE2 (but at 30 knots, just as fast) and more than triple the size of the ill-fated Titanic, built in 1912. It would take a sizeable and determined iceberg to sink her.
The QM2 has an art gallery, with 300 works on show; a theatre with 1,000 seats; a ball-room; a thalassotherapy clinic; a planetarium; 2,000 bath-rooms and no fewer than 3,000 telephone lines.
There will be 1,300 crew members and 3,000 passengers - paying between £1,000 and £20,000 for the six day crossing between Southampton and New York. The most luxurious single cabin is split-level and 209 metres square, with a view of the ocean equivalent to that commanded by Captain Ronald Warwick from the bridge.
This afternoon, she will set sail for Vigo in northern Spain, for a final sea trial before she reaches Southampton for the first time on Saturday.
"She is a magnificent ship. Top of the range," said Georges Azouze, head of France's leading cruise company, Costa Croisières. But he added: "The problem is that the cruise industry is trying to get away from its old fashioned and expensive image and the Queen Mary takes us straight back there. She is based on nostalgia for the Titanic. That's not going to attract the new customers we need."
Peter Shanks, senior vice-president of Cunard, gave a more positive view: "QM2 will be the finest transatlantic, ocean liner ever. We are confident that she will stun guests when they board for the first time in January."
But the QM2 will not retain her record as the world's largest passenger ship for long. The Royal Caribbean cruise line, competitor to Cunard, has recently placed an order for a 160,000-tonne, 3,600 passenger vessel with the Masa shipyard in Finland, one of Saint-Nazaire's great rivals. The Ultra-Voyager - perhaps significantly - will be a slow, floating resort, not a speedy liner.