The captain of a U.S. aircraft carrier grappling with a coronavirus outbreak made an unusual appeal to the Navy to move thousands of sailors into quarantine on shore, illustrating the difficulty of containing the virus on crowded military vessels.

In a March 30 letter first made public by the San Francisco Chronicle, Navy Capt. Brett Crozier, commanding officer of the USS Theodore Roosevelt, asked that 90 percent of the ship’s crew of more than 4,000 sailors be moved into isolation on Guam, where the ship has been located since a spate of coronavirus infections emerged on his ship.

“Decisive action is required. Removing the majority of personnel from a deployed U.S. nuclear aircraft carrier and isolating them for two weeks may seem like an extraordinary measure,” he wrote. “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.”

The ship, which in recent months had been conducting operations in Asia, pulled into port late last week in Guam, where infected sailors and others who had close contact with them were moved onshore for monitoring or treatment. It had previously made a port stop in Vietnam, though it is not clear whether sailors were initially infected there.

While the Navy has since announced plans to test the Roosevelt’s entire crew, Crozier said that step would be inadequate because, he said, it would be impossible to implement government isolation and distancing guidelines aboard a carrier.

“Due to a warship’s inherent limitations of space, we are not doing this. The spread of the disease is ongoing and accelerating,” he wrote.

Crozier enumerated some of the problematic elements of life abroad a carrier: shared bathrooms, shared sleeping quarters, group mealtimes, work tasks that require individuals to remain in proximity, ladders and other surfaces that are frequently touched as crew members move around the ship.

A fifth of those initially diagnosed with the virus, Crozier said, had tested negative one to three days before coming down with symptoms.

In his letter, Crozier proposed that approximately 10 percent of the crew remain onboard to tend to the ship’s nuclear reactor and take care of other core duties. To bolster his case, the captain cited research showing how conditions aboard the Diamond Princess cruise ship, the site of an earlier outbreak, allowed the virus to spread at an accelerated rate.

It was not immediately clear to whom the letter was addressed or who would grant permission for such a move. The Roosevelt is one of 11 American aircraft carriers.

The predicament facing naval commanders is just one aspect of the challenge in front of Pentagon leaders as they seek to help civilian authorities respond to the coronavirus crisis in the United States, while also maintaining overseas security missions and minimizing the disease’s effect on service members.

Thomas Modly, the acting Navy secretary, said in an interview on CNN that he heard about Crozier’s letter Tuesday morning.

“We’ve been working actually the last several days to move those sailors off the ship, and to get them into accommodations in Guam,” Modly said. “The problem is that Guam doesn’t have enough beds right now, and so we’re having to talk to the government there to see if we can get some hotel space or create some tent-like facilities there.”

Modly said Navy leadership “does not disagree” with Crozier but wants to handle the situation in a methodical way.

Evacuating a warship is not the same as taking passengers off a cruise ship, he said, citing the need to watch over weapons and be prepared to fight fires aboard the ship. The Navy is moving to accelerate the testing of those aboard the vessel and wants to clean the entire carrier, he said.”We’re absolutely accelerating it,” Modly said.

Defense Secretary Mark Esper said Tuesday night on CBS News that he had not yet read Crozier’s letter but that “I don’t think we’re at that point” where it makes sense to evacuate the ship.

Navy officials did not immediately provide a current number for how many of the Roosevelt’s crew have tested positive for the disease. The Chronicle, citing a senior officer aboard the ship, said that more than 100 sailors have tested positive. Navy officials have said previously that dozens of cases were confirmed.

A Navy official, speaking on the condition of anonymity to discuss an evolving situation, said Crozier had alerted leaders of the military’s Pacific Fleet on Sunday to “continuing challenges in isolating the virus,” urging the Navy to place more of the ship’s crew in facilities that allow for greater isolation.

Jim Stavridis, a retired Navy admiral, said in an email that naval vessels are “ideal breeding grounds for the spread of viruses” because it is impossible to do social distancing on them. The problem, he said, is compounded because the service cannot just tie up the carrier and send everyone ashore.

“It is full of weapons, billions of dollars of equipment, fire hazards and nuclear reactors,” he said.

There is a critical need for testing and getting those known to be infected ashore immediately, Stavridis added. Reducing the crew also will help space out sailors. But Stavridis said U.S. officials should expect similar incidents in the future.

“The best advice for the Pacific Fleet and indeed the entire U.S. Navy is test, test and test,” and then remove those infected as soon as possible, he said.

As ships with infections come offline, other ships must be surged forward to replace them, said Stavridis, who is now an operating executive with the Carlyle Group investment firm.

In a conference call with reporters, the commander of the U.S. Pacific Fleet, Adm. John C. Aquilino, said Tuesday that the Navy will continue to take care of sailors aboard the Roosevelt and that his top priority is their health. So far, no sailors have required hospitalization, he said.

Aquilino, asked about the captain’s letter, said he is “welcoming feedback” during a dynamic situation and wants to “make sure that we understand what the leader on the ground needs.”

Aquilino said the Navy has been working toward what they believe the crew needs, and toward having the capacity to quarantine a large number of sailors. He’s “optimistic” that the ability to do so will be delivered, “shortly,” he said, without providing a more specific timeline. But Aquilino said there “has never been an intent” to take all sailors off the ship, and that if the carrier needed to respond to a crisis today, it would.

In his letter, Crozier also said the Roosevelt could embark and fight immediately if required.

“But in combat we are willing to take certain risks that are not acceptable in peacetime,” he wrote.

The mother and father of a sailor on the ship who tested positive for the coronavirus said in an interview with The Washington Post that despite the leadership of the carrier ringing alarm bells, higher-ups at the Navy had been “dragging their feet.”

The parents, who spoke on the condition that their names not be used to avoid identifying their child, said the Navy should have immediately tested the entire crew and separated those who tested positive to contain the outbreak.

Instead, they said, their child tried for days to get a test and was denied, despite having interacted with someone known to have come down with the virus. Only after their child was showing full-blown symptoms was a test offered. When it came back positive, their child was removed from the ship and put in military base housing in Guam.

The Navy first evacuated essential personnel, including those without symptoms, according to the parents. Only afterward were some sailors who weren’t “essential” to the ship’s operations given the possibility to disembark.

“What it boils down to is why didn’t they test everyone right away,” the mother of the sailor said, saying that an effort to test the entire ship immediately could have helped contain the outbreak after it first became apparent.