When three Chinese scientists plunged to the bottom of the South China Sea in a tiny submarine early this summer, they did more than simply plant their nation’s flag on the dark seabed.

The men, who descended more than two miles in a craft the size of a small truck, also signaled China’s intention to take the lead in exploring remote and inaccessible parts of the ocean floor, which are rich in oil, minerals and other resources that the Chinese would like to mine. And many of those resources happen to lie in areas where China has clashed repeatedly with its neighbors over territorial claims.

After the flag planting, which was done in secret but recorded in a video, Beijing quickly turned the feat of technology into a show of bravado.

“It is a great achievement,” Liu Feng, director of the dives, was quoted as saying by China Daily, an English-language newspaper, which telegraphs government positions to the outside world.

The global seabed is littered with what experts say is trillions of dollars’ worth of mineral nodules as well as many objects of intelligence value: undersea cables carrying diplomatic communications, lost nuclear arms, sunken submarines and hundreds of warheads left over from missile tests.

While a single small craft cannot reel in all these treasures, it does put China in an excellent position to go after them.

“They’re in it for a penny and a pound,” said Don Walsh, a pioneer of deep-ocean diving who recently visited the submersible and its makers in China. “It’s a very deliberate program.”

The sea dragon

The small craft that made the trip – named Jiaolong, after a mythical sea dragon – was unveiled publicly late last month after eight years of secretive development. It is designed to go deeper than any other in the world, giving China access to 99.8 percent of the ocean floor.

Technically, the Jiaolong is a submersible. These undersea craft differ from submarines in their small size, their need for a mother ship on the surface, and their ability to dive extraordinarily far under the waves despite the inky darkness and the crushing pressures. The world has only a few.

Jiaolong is meant to go as deep as 7,000 meters, or 4.35 miles, edging out the current global leader. Japan’s Shinkai 6500 can go as deep as 6,500 meters, outperforming craft “all over the world,” according to its makers. Russia, France and the United States lag in the game of going deep.

U.S. experts familiar with the Chinese undersea program say it is unusual in that China has little experience in the daunting field. As a result, China is moving cautiously. Jiaolong’s sea trials began quietly last year and are to continue until 2012, its dives going deeper in increments.

“They’re being very cautious,” Walsh said. “They respect what they don’t know and are working hard to learn.”

In an interview, Walsh said that the Chinese were especially interested in avoiding the embarrassment of a disaster that ends with the aquanauts’ entrapment or death. “If I’m the new kid on the block,” he said, “I’m going to make sure that I’ve got bragging rights.”

Staking out claims

Still, China is already waving flags. The move resembles how Russian scientists, in the summer of 2007, plunged through the ice pack at the North Pole and planted their flag on the bottom of the ocean. Upon surfacing, the explorers declared that the feat had strengthened Moscow’s claims to nearly half the Arctic seabed.

Wang Weizhong, a Chinese vice minister of science and technology, said that the Jiaolong’s sea trials “marked a milestone” for China and global exploration. The recent successes of the craft, he said in late August at a news conference in Beijing, “laid a solid foundation for its practical application in resource surveys and scientific research.”

But at least one senior Chinese expert questioned what he called “the current propaganda.” The expert, Weicheng Cui, a professor at the China Ship Scientific Research Center, which is building the submersible, said Thursday in an e-mail that the craft’s sea trials had steered clear of contested islands “to avoid any diplomatic issues.”

The flurry of publicity over the flag planting, he said, “is not so helpful for us to complete the project.”

China’s splash in the arcane world of submersibles comes after years of singling out major industries and technologies for rapid development. China is rushing to make supercomputers and jumbo jets. With expanding political ambitions and territorial claims in neighboring seas, it has paid special attention to oceanography and building a blue-water navy, one that operates in the deep waters of open oceans.