The USS Connecticut (SSN-22) suffered a submerged collision with an unidentified object in international waters in the South China Sea last Saturday. At least 11 sailors were injured in the incident with moderate to minor injuries.

“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. The safety of the crew remains the Navy’s top priority. There are no life-threatening injuries,” Capt. Bill Clinton told USNI News on Thursday.

The submarine is traveling on the surface to port in Guam.

“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 U.S. Navy has not requested assistance. The incident will be investigated.”

Navy officials told CNN that the vessel remains fully operational. AP news agency quoted the officials as saying it was unclear what the submarine hit but it was not another sub. One said it may have been a sunken ship, container, or another uncharted object.

The incident takes place while tensions in the region soar. China a “record number” of military jets into Taiwan’s air defense zone for four days in a row. On Saturday, 39 Chinese warplanes entered Taiwan’s ADIZ. Taiwan responded by scrambling jets and deploying air defense missiles to monitor the aircraft. On Monday, China sent 56 aircraft into Taiwan’s ADIZ within 24 hours. China considers Taiwan to be its province while Taiwan considers itself to be independent. The USS Connecticut was part of a multinational maritime show of force in the South China Sea including ships from the US, UK, Japan, Australia, Canada, and the Netherlands. The exercise included three aircraft carrier strike groups.

Launched in 1997, Connecticut is one of three Sea Wolf-class boats that were commissioned during the Cold War as attack submarines designed to hunt Soviet submarines. The last time a U.S. Navy submarine is known to have had a serious collision was in 2005 when the USS San Francisco hit an undersea mountain at full speed. That crash left one sailor dead and most crew members injured. The captain and several other senior officers were relieved of their duty, as it emerged that they had been using outdated seafloor charts, despite having up-to-date maps available.