WASHINGTON (AP) — The captain of a U.S. Navy aircraft carrier facing a growing outbreak of the coronavirus is asking for permission to isolate the bulk of his roughly 5,000 crew members on shore, which would take the warship out of duty in an effort to save lives.

In a memo to Navy leaders, the captain of the USS Theodore Roosevelt said the spread of the disease is ongoing and accelerating, and said that removing all but 10% of the crew is a “necessary risk” in order to stop the spread of the virus. The ship is docked in Guam.

U.S. Navy leaders on Tuesday were scrambling to determine how to best respond to the extraordinary request as dozens of crew members tested positive.

“We are not at war. Sailors do not need to die. If we do not act now, we are failing to properly take care of our most trusted asset our sailors,” said its Navy Capt. Brett Crozier, in a memo obtained by The Associated Press.

A U.S. Navy official said Crozier alerted commanders on Sunday evening of the continuing challenges in isolating the virus. The official, who spoke on condition of anonymity to discuss internal deliberations, said Crozier wants more isolated housing for the crew and that Navy leadership is reviewing options to ensure the health and safety of the crew.

Acting Navy Secretary Thomas Modly told CNN that they are doing the best they can to “adjust on the fly” and take care of sailors on the carrier.

“The key is to make sure that we can get a set of crew members that can maintain all those critical functions on the ship, make sure that they’re clean, and then get them back on while we clean the ship and get the other crew members off,” he said.

In Asia, a carrier presence is central to what the Pentagon has identified as a fundamental shift from fighting insurgent and extremist conflicts in the Middle East to a return to “great power competition.” That means, principally, a bigger focus on China, including its militarization of disputed areas of the South China Sea.

The outbreak on the carrier may be the Navy’s most dramatic, but it tracks an accelerating upward trend across the military. The Pentagon said the number of cases in the military reached 673 on Tuesday morning, a jump of 104 from the day before and up from 174 a week ago.

Since March 20, the total has surged tenfold, even as the Pentagon has taken many steps to try to limit the spread, including halting nearly all movement of troops overseas.

The carrier, like other Navy ships, is vulnerable to infectious disease spread given its close quarters. The massive ship is more than 1,000 feet long; sailors are spread out across a labyrinth of decks linked by steep ladder-like stairs and narrow corridors. Enlisted sailors and officers have separate living quarters, but they routinely grab their food from crowded buffet lines and eat at tables joined end-to-end.

Listing many of those problems, Crozier’s memo, which was first reported by the San Francisco Chronicle, warns that the close quarters means that thousands of sailors now require quarantine. He said sailors have been moving off the ship into shore-based quarters, but much of that is also not adequate. He said much of the off-ship locations available so far are group quarantine sites, and already two sailors housed in an auditorium have tested positive for the virus.

To stop the spread of the virus and prevent death, Crozier said they must take a methodical approach, move the majority of the sailors off the ship, isolate them and completely clean it. He said about 10 percent of the crew would have to stay on board to secure the vessel, run critical systems and sanitize everything.

While that may seem like an extraordinary measure, he said it is a necessary risk.

“It will enable the carrier and air wing to get back underway as quickly as possible while ensuring the health and safety of our sailors,” Crozier said, adding that finding appropriate isolation for the crew “will require a political solution but it is the right thing to do.”

Modly told CNN that efforts are underway to help the ship, while also ensuring that the Navy and the U.S. military continue to protect the country.

“This is a unique circumstance,” he said. “And we’re working through it and trying to maintain that proper balance to ensure that our friends and allies, and most importantly our foes and adversaries out there, understand that we are not standing down the watch.”

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AP National Security writer Robert Burns contributed to this report.