Was the doomed US submarine caught in a monstrous whirlpool in the South China Sea?

BEIJING: It’s the stuff of science fiction. A giant whirlpool, stretching hundreds of miles, suddenly appears in the ocean, threatening anything in its path.

But now, following the declassification of a Chinese operation, it appears this particular maelstrom was all too real. And it could be the explanation behind an international incident involving an American nuclear-powered submarine.

Underwater whirlpools pose an additional danger because they cannot be seen. Known as deep eddies, they are produced by ocean currents that flow around terrain features such as seamounts (submerged mountains). They do not affect surface transport, but they constitute a danger to underwater navigation, as demonstrated in the past.

In September 2021, China launched a massive operation to hunt and record a huge whirlpool, more than 200 km (124 miles) in diameter, that appeared east of the Paracel Islands in the South China Sea.

China’s most advanced research vessel and largest fleet of drones ever assembled were sent to carry out comprehensive tracking of this vortex in the air, on the sea surface and underwater.

Around the same time, the USS Connecticut, a Seawolf-class nuclear-powered fast attack submarine operated by the U.S. Navy, was also in the area.

On October 2, 2021, it hit an unknown object and had to make an emergency breach. It suffered serious damage, with repairs ongoing to this day.

The USS Connecticut (SSN-22) was traveling at 24 knots when it was involved in the serious accident. A subsequent US military investigation placed the blame on the negligence of the officers and crew on board, as well as their unfamiliarity with the terrain.

A Seawolf-class attack submarine, a submarine as large as the SSN-22 is considered one of the most powerful underwater combat platforms in the US Navy. He can maintain silence even at high speeds, making it difficult for enemies to distinguish his sound signature from the background noise of the ocean.

The team of researchers, led by engineer Li Yuhang from the 713th Research Institute of China State Shipbuilding Corporation, used real-world environmental data collected by Chinese sensors in the South China Sea to observe the water surface wake in an attempt to “offer some suggestions for the safe navigation of Chinese submarines”.

They detailed their research in a peer-reviewed paper published in the Chinese Journal of Theoretical and Applied Mechanics on May 27.

When a submarine moves, it inevitably disturbs the surrounding water. Part of this disturbance reaches the ocean surface and can be detected by aircraft or satellites equipped with high-resolution radar.

These fine ripples can provide clues to important information such as the submarine’s position, speed, direction or even make. However, the formation and propagation of these waves are greatly influenced by environmental factors such as ocean currents, temperature and salinity, resulting in significant differences in signal intensity and patterns in different maritime areas.

Due to military sensitivity, publicly available research in the past has focused on theoretical models, avoiding real-world data.

“Currently, research on the surface wake of (underwater) water in the real ocean is still relatively scarce,” Li and his colleagues wrote in their paper.

The novelty of Li’s work lies in the use of real data from the South China Sea for the first time. This allowed scientists and engineers to conduct “systematic research into the characteristics of the water surface response wave field excited by submarines in the real ocean.”

And they got some unexpected results.

The team’s study area focused on the Dongsha Islands, southwest of Taiwan. The Dongsha Islands, also known as the Pratas Islands, are one of the most important underwater passages in the northern South China Sea and are frequently visited by People’s Liberation Army (PLA) anti-submarine aircraft during military exercises against Taiwan.

While navigating this area, Chinese researchers discovered that submarines about 100 meters long (328 feet) and more than 10 meters in diameter – similar to the size of SSN-22 – can resonate with the surrounding water, causing unexpected disturbances.

When the depth of the submarine is 100 meters and the speed exceeds 20 knots, a large number of ripples with heights of up to several centimeters can be generated on the ocean surface, according to estimates.

The Seawolf-class submarine can reach a maximum cruising speed of 25 knots, according to the Submarine Industrial Base Council, which involves more than 5,000 American companies that supply critical materials to U.S. submarine programs.

The SSN-22’s speed reading before the collision appeared in a footnote to the U.S. military investigation report released in 2022. Investigators said the Connecticut was traveling at high speed in the South China Sea as it headed toward Okinawa to a “humanitarian evacuation”. ”When the accident occurred.

Although the Seawolf class is the most advanced attack submarine in the U.S. military, its design was completed 40 years ago, when detecting surface ripples relied primarily on visual observation. High-speed cruising was considered safe, even close to the enemy coast.

Increasing the depth of the submarine can also reduce surface waves. But in recent years, wake detection technology has made rapid progress. According to a maritime test announced by Chinese scientists in August last year, a new type of anti-submarine radar based on 6G technology can detect underwater ripples as small as tens of nanometers on the rippled sea surface.

On May 20, researchers from the Chinese Naval University of Engineering published a paper claiming that artificial intelligence technology can help detect underwater wakes in complex maritime conditions with 96% accuracy.

But that doesn’t mean a submarine is always safe at lower speeds. Li’s team found that significant resonance can also occur when the submarine travels at about two knots, increasing the risk of position exposure.

This particular discovery could add another challenge to any potential undersea warfare in the South China Sea. Before launching a surprise attack against land or sea targets, submarines generally need to enter predefined positions at speeds of two to eight knots and rise to a depth of less than 100 meters to launch submarine-launched missiles, according to some military experts.

If a submarine’s position is exposed during this period, it could have disastrous consequences, they said.

Anti-submarine forces rely on different reconnaissance platforms to confirm a target, including traditional sonars, seafloor sensor networks, air-based geomagnetic anomaly detectors, high-precision gravity detectors, and lasers.

Significant progress and advancements have been made by scientists and engineers in detection technology in these areas in recent years, posing serious challenges to the stealth combat capabilities of traditional submarines.