The fast-attack submarine USS Connecticut (SSN 22) transits ahead of American and Japan Self-Defense Forces (JMSDF) ships at the end of ANNUALEX 19G, the maritime component of the U.S.-Japan exercise Keen Sword '08. Credit: US Navy photo.

Deep in the dark depths of the world’s ocean, things can go bump in the night.

Other submarines, whales, unknown seamounts, even UFOs can be found in the deepest reaches.

Chalk this one up to an X-File … if officials are telling the truth, it may never be solved.

According to USNI News, almost a dozen sailors have been injured after a US nuclear attack submarine hit an unknown underwater object in the South China Sea.

The Seawolf-class nuclear attack submarine USS Connecticut (SSN-22) suffered an underwater collision while operating in international waters on Oct. 2 and has returned to Guam, port for the US 7th Fleet, a US Pacific Fleet spokesman said.

“The Seawolf-class fast-attack submarine USS Connecticut (SSN-22) struck an object while submerged on the afternoon of Oct. 2, while operating in international waters in the Indo-Pacific region,” Capt. Bill Clinton told USNI News.

The safety of the crew remains the Navy’s top priority. There are no life-threatening injuries,” he said.

“The submarine remains in a safe and stable condition. USS Connecticut’s nuclear propulsion plant and spaces were not affected and remain fully operational.

“The extent of damage to the remainder of the submarine is being assessed. The US Navy has not requested assistance. The incident will be investigated.”

A defense official told USNI News about 11 sailors were hurt in the incident with moderate to minor injuries.

China claims almost all of the resource-rich South China Sea, through which trillions of dollars in shipping trade passes annually, with competing claims from four south-east Asian states as well as Taiwan.

Compared to previous Los Angeles Class submarines, Seawolf Class submarines are larger, faster, and significantly quieter. The boats also have extensive equipment to allow for “littoral”, or “shallow-water” operations. Credit: US Navy.

Beijing has been accused of deploying a range of military hardware there, including anti-ship and surface-to-air missiles, and ignored a 2016 international tribunal decision that declared its historical claim over most of the waters to be without basis.

Navy officials told the Washington Post it is not believed that China caused the collision and that the vessel was monitored by other US vessels in the region as it moved to Guam.

The 7th Fleet’s statement said that the Navy had “not requested assistance,” while a DOD official quoted by USNI News said the submarine had steamed to Guam “on the surface.”

A US official confirmed to NPR that the Connecticut had arrived in port.

“As the party involved, the US should clarify in detail the situation of the accident, including the location, the intention of the sailing, details of the accident, such as what exactly it collided with, whether it caused a nuclear leak, and whether it damaged the local marine environment,” Foreign Ministry spokesperson Zhao Lijian told reporters

Zhao said the accident exposed the “serious threat and significant risk to regional peace and stability” posed by U.S. naval operations in the South China Sea aimed at challenging China’s claim to virtually the entire strategic waterway.

He also accused the US of delaying the release of information about the collision, and he reiterated China’s objections to a deal announced last month to provide Australia with nuclear-powered submarines in what Beijing sees as part of a campaign to counter its rising military and economic power in Asia.

“The US side should abandon its old cold war and zero-sum thinking and narrow geopolitical concepts and stop this wrong approach that undermines the peaceful and stable development of the region,” Zhao said.

The US Navy has three Seawolf Class submarines.

Commissioned on July 19, 1997, USS Seawolf (SSN 21) is exceptionally quiet, fast, well-armed, and equipped with advanced sensors. Though lacking Vertical Launch Systems, the Seawolf class has eight torpedo tubes and can hold up to 50 weapons in its torpedo room.

The third ship of the class, USS Jimmy Carter (SSN 23), has a 100-foot hull extension called the multi-mission platform.

This hull section provides for additional payload capacity to accommodate advanced technology used to carry out classified research and development and for enhanced warfighting capabilities.

The last time a US submarine is known to have struck an underwater object was in 2005, when the USS San Francisco hit a seamount, or underwater mountain, near Guam while traveling at full speed.

The sailors aboard were thrown as far as 20 feet by the impact, and the majority of the 137 aboard were injured in the incident, with one killed.

A subsequent investigation determined that the submarine’s charts of the seafloor did not show the seamount.

Sources: USNI News, NPR, Washington Post, The Guardian, Military.com