A civilian approaching a Navy destroyer at the world’s largest naval base late at night took a weapon from a sailor who was standing watch and used it to shoot and kill another sailor who tried to intervene, Navy officials said Tuesday.

Navy security forces then killed the suspect, who was authorized to be on Naval Station Norfolk and did not bring his own weapon on base, according to Capt. Robert Clark, the base’s commanding officer.

The identities of the civilian and the sailor who were killed have not been released.

“Information about our sailor will come at the appropriate time and today is not that day,” said Clark, who asked for privacy for the sailor’s family.

No other injuries were reported from the encounter, which occurred Monday about 11:20 p.m. on the USS Mahan, a guided-missile destroyer that had recently returned from a port visit in New Orleans during Mardi Gras. It wasn’t immediately clear why the civilian approached the ship or if he ever had access to it previously.

The Navy said the civilian was coming toward the ship’s quarterdeck, which is traditionally the ceremonial entry point aboard a ship, when the struggle ensued and the civilian was able to disarm the Petty Officer of the Watch.

Clark said the identification found with the civilian indicates it is unlikely he was a military dependent authorized to be on base for that reason. He said the civilian was found with a TWIC card.

A TWIC is a transportation worker’s credential and is issued by the Transportation Security Administration to personnel who require unescorted access to secure areas, such as truck drivers. The cards are valid for five years, according to the TSA. All merchant mariners are also required to have a TWIC card, including employees of the Navy’s Military Sealift Command.

Military Sealift Command hires civilian mariners to crew its ships, including the hospital ship USNS Comfort, which uses the same pier as the Mahan. Clark said it was unclear what exactly the civilian’s job was or when he worked on the base.

The base was briefly on lockdown following the shooting, but traffic was back to normal early Tuesday morning.

The Navy will release both men’s names after their families are notified, said Naval Station Norfolk spokeswoman Terri Davis.

Aside from the pier where the Mahan was docked, operations had returned to normal at the base, with counselors available, the Navy said in a statement.

But most enlisted sailors on the Mahan — docked at the first of 13 main piers — were told not to report to duty Tuesday.

Some sailors gathered for a training session — unrelated to the shooting — and began with a moment of silence for the fallen sailor. “We’ll find out what happened, and we’ll prevent that from occurring again,” said Adm. Bill Gortney, commander of U.S. Fleet Forces Command.

The shooting on the Mahan comes about a month after the Navy held anti-terrorism and force protection exercises on bases around the U.S., including an active-shooter drill at the Norfolk station.

To get on the base, civilians must be escorted or have identification that allows them to be there. Authorized civilians can include Department of Defense employees, contractors and military family members.

Each base entrance is guarded, and motorists present IDs. Inspections are rare. All 13 piers have additional security forces. As part of ongoing security efforts, handheld ID scanners were implemented this year at Navy bases in the region, including the Norfolk station.

The shooting comes months after a September incident at the Washington Navy Yard, in which a gunman — identified as a contractor and former Navy reservist — killed 12 civilian workers before being shot to death.