A US nuclear submarine's mysterious collision with an object in the South China Sea suggests it was lurking near the bottom, expert says

• A US Navy submarine collided with an object in the Indo-Pacific, the Navy revealed Thursday.
• A former Navy submariner told Insider reports suggest the submarine was operating along the sea floor.

The US Navy Seawolf-class submarine USS Connecticut collided with an unknown object in the South China Sea recently, damaging the powerful fast-attack boat and injuring nearly a dozen crew members.

The US Navy statement on the collision said specifically the Connecticut collided with an "object," and service officials talking with Navy Times indicated it was not another vessel and not likely to have been a land mass.

Navy officials told the Associated Press that the object the submarine hit might have been a sunken ship, a shipping container, or some other uncharted object.

Public details on the incident are still very limited, but a former US Navy submariner and defense expert told Insider reports on the collision indicate the submarine was probably operating close to the bottom, possibly on a surveillance mission.

The South China Sea is already a challenging operating environment for submarines because it is, for the most part, actually quite shallow, especially compared to the waters of the nearby Pacific Ocean, with depths of thousands of feet.

Comments from Navy officials speculating that the nuclear-powered submarine may have collided with a container or shipwreck suggests that the ship was not only in shallow waters but likely close to the sea floor, said Bryan Clark, a senior fellow at the Hudson Institute.

And reports that only about a dozen crew members suffered only minor injuries suggest the submarine may have been moving slowly, possibly because it was near the bottom or possibly to remain undetected or both.

"The things you might do near the sea floor are hide, if you are just trying to surveil Chinese submarine operations, or try to put something on the sea floor or pick something up, which might be a sensor," explained Clark, who is a retired submarine officer and former special assistant to the chief of naval operations.

A potential point of interest for surveillance would be Yulin Naval Base on Hainan Island, from which China operates an unknown number of submarines.

Beyond surveillance, other possible operations could include activities like sea floor mapping.

Clark told Insider he "would not be surprised if the Connecticut was up there doing some kind of surveillance operation on Chinese submarine operations out of Hainan Island and it was close to the bottom because it was trying to hide and it ran into something while it was doing that."

It is unclear what kind of operations the Connecticut was conducting at the time of the collision, but a Navy official characterized them to the AP as routine.

The challenge with operating near the sea floor is that there is debris down there that can pose a threat to the submarine.

For instance, the South China Sea is an important strategic waterway through which trillions of dollars in global trade pass each year, and shipping containers are frequently lost at sea.

Submarines have a rudder and use water and compressed air in ballast tanks to control its depth.

And "you can operate fairly closely to the sea floor pretty competently because you have good maps and you've got a bathometer that's measuring the distance between you and the sea bottom," Clark said, explaining that topography charts, depth senors, and passive sonar allow a submarine to steer clear of most obstacles.

But if there is a big uncharted object, like a massive shipping container possibly standing on end, the submarine may not be able to detect it until it is right on top of it.

"That's the problem you run into with operating near the sea floor in an area like that, where there's lots of objects on the sea floor," Clark said.

The Navy is conducting an investigation into the submarine collision, an uncommon occurrence that happened on October 2 but was not reported until five days later due to concerns about operational security, according to the Associated Press.