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PANAMA CITY – More than 100 years ago when the SS Ancon sailed into the history books as the first ship to transit the Panama Canal, the waterway was a display of American ingenuity and the Panama Canal Zone was firmly in U.S. hands.

But the ship making the first official trip through the newly expanded canal Sunday will be a Chinese megaship. The United States completely withdrew from the canal on Dec. 31, 1999, and there was barely any U.S. participation in the $5.5 billion canal project, which will allow the world's bigger ships to transit Panama's "highway of the sea."

The United States remains the most important user of the canal and canal officials say it will be for the foreseeable future, but world trade patterns have shifted in the past century and China has become the world's largest trading nation.

Between 6 and 7 a.m. on Sunday, China COSCO Shipping's recently renamed 984-foot-long Panama will approach the new Agua Clara locks on the Atlantic side of the 50-mile-long canal to begin the first official voyage through the expanded canal. It won the honor in a drawing among the canal's top customers.

Although the new locks — tall as an 11-story building — are an engineering marvel and the expansion is expected to double the canal's capacity, it's been a long slog. The project is being delivered nearly two years behind schedule and various claims by the Grupo Unidos por El Canal, the international consortium that built the expansion, could push the price for the project even higher. The Panama Canal Authority also has its own counterclaims.

But now — 110 million man hours, 292,000 tons of structural steel, 1.6 million tons of cement and 5 million cubic meters of concrete later — the project is finished.

"This is a great project from an engineering and logistical point of view," said Giuseppe Quarta, chief executive of the consortium.

The project, which got underway in 2007, included deepening and widening the entrances to the canal, deepening and widening the navigational channel through Gatun Lake, deepening the channel at Culebra Cut, raising the level of the lake, building a new 3.8-mile Pacific access channel, and construction of larger Atlantic and Pacific locks that are as long as three Empire State Buildings laid end to end.

With the expansion able to handle longer, wider and heavier ships, the canal authority hopes to win back shipping lines that switched to the Suez Canal or used U.S. West Coast ports because their ships couldn't fit through the original locks inaugurated on Aug. 15, 1914.

As he watches the Chinese ship finally enter the locks on Sunday, Manuel E. Benitez, deputy administrator of the canal authority, said, "I'll be a happy man."