A COVID-19 outbreak occurred aboard the Pearl Harbor-based missile destroyer USS Michael Murphy, forcing crew members to quarantine and a brief suspension of operations for the ship, the Navy confirmed Thursday.

NBC News reported Thursday that nearly a quarter of the ship’s 300 crew members had tested positive.

The infected sailors, who began testing positive on Nov. 4, were placed in isolation while all close contacts and nonessential crew members self-isolated for two weeks “out of an abundance of caution,” the Navy said in a statement.

Navy officials declined to provide exact numbers due to the Pentagon’s policy restricting commanders from reporting infections at the local level, but they confirmed there was a “cluster of infections” on the ship.

Almost all members of the crew who tested positive were asymptomatic and were expected to return to duty.

“Most of them will be coming out of isolation over the weekend,” said Cmdr. Nicole Schwegman, a spokeswoman for Surface Forces Pacific.

The ship’s crew has been doing training that was interrupted by the outbreak, but the Murphy isn’t scheduled for any deployments until next year.

The military shares its cases in the state with the Hawaii Department of Health, which includes them in the state’s total case numbers. Hawaii state officials have agreed to keep those numbers secret. Pentagon officials have told the DOH that they would terminate information sharing if state officials discuss military case numbers.

The health department did not immediately respond to a request for information about when the ship’s cases may have been included in the daily count for Oahu.

“On this ship docked at Pearl Harbor, you have about a quarter of the people testing positive. It just tells you in close quarters, this virus spreads quickly,” Honolulu Mayor Kirk Caldwell said in response to a question during a press conference. “My heart goes out to the men and women who serve on that ship.”

It’s not the first outbreak in the Pacific. In March the virus began making its way through the aircraft carrier USS Theodore Roosevelt after a port call in Vietnam.

In total, 1,156 members of the carrier’s 4,779 sailor crew became infected and one died. Several members of the ship’s crew were eventually brought ashore in Guam and many were quarantined in hotels. The ship and its crew have since returned to duty.

“I would say we’ve learned the lessons of the Roosevelt,” Schwegman said. She said that in the current environment, instances of positive cases are inevitable and that early intervention is key.

In the aftermath of the Roosevelt outbreak, some Hawaii activists and lawmakers called for the military to suspend training exercises.

In particular the biennial exercise RIMPAC — the world’s largest naval exercise — attracted more scrutiny than usual over fears sailors from around the world would descend on Honolulu and spread the disease. In April, Honolulu City Councilman Ron Menor introduced a resolution requesting that the Pacific Fleet call off the exercise.

The Pacific Fleet had hoped RIMPAC 2020 would be the largest iteration of the exercise yet, but ended up hosting a heavily scaled down event with no shore leave or amphibious maneuvers, keeping the exercise entirely at sea.

None of the ships participating in RIMPAC reported outbreaks during the exercise, but two Philippine Navy sailors and a member of the Japan Maritime Self Defense Force tested positive and were quarantined before their ships set sail for Hawaii.

Civil Beat reporter Christina Jedra contributed to this article