The illness caused by the novel coronavirus continues to infect crew members from a Navy aircraft carrier, but many of them showed no signs of having the disease, a fact that highlights the importance of widespread testing as military personnel likely spread the virus to their comrades without knowing it.

The number of sailors assigned to the carrier Theodore Roosevelt who have tested positive for COVID-19, the illness caused by the coronavirus, jumped to 655 on Thursday. Two days earlier, Defense Secretary Mark Esper told reporters that only about 213 of the crew members showed any symptoms.

That means only about a third of the 585 crew members who'd tested positive at the time were symptomatic.

Related: Recruits Who Carried COVID-19 to Boot Camp Had Passed Temp Checks, Screenings

"Think about that. There are people who have tested positive -- over 300 -- who are just moving around," Esper said. "The same could apply for all of us."

Medical experts have warned that one of the dangers in the global pandemic is that COVID-19 can unwittingly be spread by "carriers," or people who are asymptomatic or have very mild symptoms.

The coronavirus has infected more than 2 million people globally and killed more than 26,000 Americans. That includes one sailor from the Roosevelt.

Esper said Pentagon officials are looking at ways to expand testing across the military, focusing on units that are deployed or are about to deploy.

"We've had a couple of meetings on that," he said. "Right now, the key is expanding the test kits, making sure that we ... have what we need to address people who are symptomatic first, but then again tiering our forces because we have to maintain that mission readiness."

The Defense Department can currently complete about 9,000 tests per day in its labs, Joint Chiefs Chairman Army Gen. Mark Milley said. In the next 45 days, they want to rapidly increase that to 60,000 per day, he said.

"Our aspiration is to expand testing, especially for groups that are going to probably be in tighter quarters, such as sub crews, bomber crews, basic trainees, and things like that," Milley said.

The Roosevelt isn't the first place the military has seen asymptomatic people spreading COVID-19. A pair of Marine recruits in South Carolina got coronavirus screenings before boot camp and showed no symptoms for the illness before starting training only to later test positive.

Coronavirus cases there quickly began to spike, prompting the Marine Corps to order a temporary halt to incoming shipments of new recruits.

-- Gina Harkins can be reached at gina.harkins@military.com. Follow her on Twitter @ginaaharkins.

Read more: Swarm of Iranian Boats Harassed US Ships in Persian Gulf, Navy Says