The monarch was protected from showers by a large tent as she launched the $880 million vessel in front of 2,000 invited guests in the port city that was the departure point for the Mayflower (search) and the Titanic (search).
"I name this ship Queen Mary 2," said the queen, who wore a hot pink dress and matching coat and a purple hat, and was accompanied by her husband, Prince Philip. "May God bless her and all who sail in her."
She then pressed a button that released a bottle of champagne that smashed against the ship's hull.
The Right Rev. Michael Scott-Joynt, Anglican bishop of Winchester, blessed the ship and said a prayer in French for the 15 people killed in November when a gangway to the giant ocean liner collapsed in the French port of St. Nazaire, where it was built. Most of the dead were ship workers' relatives invited to visit the vessel, and members of a cleaning crew.
The ceremony mixed pomp and glitz, featuring military pipes and drums, a pop singer and an operatic rendition of "Amazing Grace."
Hundreds of Southampton residents, barred from the dockside by tight security around the launch, braved wind and rain to watch the ceremony on a large screen in a nearby park.
For some, it recalled Southampton's glory days as a major port that shipped millions of pieces of mail and hundreds of thousands of emigrants around the British empire.
The ship is named after the Queen Mary, a famously luxurious trans-Atlantic liner that came into service in 1936 and is now retired.
Queen Mary, the grandmother of the current queen, was married to King George V, who ruled from 1910 to 1936. The "2" in the name Queen Mary 2 refers to this being the second ship named after the queen.
The new cruise liner took more than five years to build. It is 1,138 feet long and 238 feet high -- as tall as a 21-story building. It will take over the trans-Atlantic duties of the Queen Elizabeth 2 ocean liner, which was launched in 1967.
Its 2,600 passengers will be able to choose from six restaurants, five swimming pools, an art gallery and a movie theater that doubles as a planetarium.
"It's amazing, isn't it?" said Anne Cross, who works for a car importer in Southampton harbor and admired the new ship during lunchtime. "The QE2 is normally in there. When you look at that and think of the QE2, it makes it look like a little toy."
Fares for Queen Mary 2's fully booked maiden voyage from Southampton to Fort Lauderdale, Fla., starting Monday, begin at $4,400 per person for 14 nights and rise to $48,310.
The vessel is owned by Cunard Lines, which belongs to the U.S. company Carnival, but it will sail under a British flag.
Cunard president Pamela Conover said the ship "represents no less than the triumph of a great British tradition of which we can all be proud."
The Queen Mary 2's title as the world's biggest ocean liner is expected to be short-lived.
Cruise operator Royal Caribbean Cruises Ltd. recently confirmed an order with Finland's Kvaerner Masa-Yards for the Ultra Voyager, which will accommodate 3,600 passengers and be bigger than the Queen Mary 2. The Ultra Voyager is expected to enter service in 2006.