Three sailors aboard the carrier Theodore Roosevelt have tested positive for COVID-19, the Navy announced Tuesday, the first cases of the disease caused by the novel coronavirus on a ship underway.

In a press conference with Acting Secretary of the Navy Thomas Modly and Chief of Naval Operations Adm. Michael Gilday, Modly announced the three cases, adding that the service was working on evacuating the sailors as soon as possible.

The spread of COVID-19 on an underway warship raises the frightening prospect of a new cluster of cases among 5,000-plus deployed sailors, and marks a new chapter in the Navy’s fight to contain the spread within its ranks. The service has documented nearly 90 cases to date, Modly said.

The Roosevelt was last in port in Da Nang, Vietnam, 15 days ago, Gilday said. The decision to go forward with the port visit in early March was made when Vietnam had only 16 total cases, all isolated in the northern city of Hanoi, he said.

It is unknown yet how the sailors may have contracted the illness, noting that aircraft land on the ship regularly from outside the command, Gilday said, but that the Navy is trying to trace the sailors’ movements and isolate sailors they’ve been in contact with.

The Roosevelt sailors have exhibited only mild symptoms so far, Gilday said.

“In those cases, those sailors are running a temperature and they have some body aches, but we wouldn’t necessarily characterize them as requiring hospitalization," he said. "But they’re positive, so we are rapidly removing them from the ship and understanding who they’ve come in contact with on the ship so we, as best we can, can try and isolate and contain.”

Despite the possibility of a wider outbreak on board, the Navy is not considering recalling the carrier or pulling it into port, Gilday said.

× Fear of missing out? Sign up for the Navy Times Daily News Roundup to receive the top Navy stories every afternoon. Thanks for signing up. By giving us your email, you are opting in to the Navy Times Daily News Roundup.

“We’re not in a position right now where we need to pull that ship in or take that ship off the front line, so this will be a day-by-day evaluation,” Gilday said.

The Navy is committed to maintaining readiness, he said.

“We’re taking this day by day and we’re being very deliberate in terms of how we do it," Gilday said of the fight to contain the spread in his ranks. “The Secretary of Defense’s priorities are taking care of people and maintaining mission readiness. And both of those go hand-in-glove in this COVID-19 environment.”