Schofield Barracks is wrapping up its biggest annual field exercise, in which soldiers battled simulated tanks and a sophisticated “near-peer” enemy — while also coping with a very real coronavirus pandemic by closely monitoring personnel in an isolated training “bubble.”

Exercise Lightning Forge, with about 5,500 soldiers, is the 25th Infantry Division’s first large-scale training exercise since a gradual return to training in early May. A company of 133 Royal Thai Army soldiers also participated.

As of Friday, the Defense Department reported 20,212 military members who’ve had COVID-19, 8,421 recovered, 425 hospitalized and three deaths as the military count has risen with civilian increases.

>> PHOTOS: Over 5K Schofield soldiers participate in large-scale training exercise on Oahu

The training focus for the two-week exercise ending Tuesday has been on the 2nd Infantry Brigade Combat Team’s 3,700 soldiers as it prepares for an October trip to the Joint Readiness Training Center at Fort Polk, La., the final step in certifying a brigade’s combat readiness.

Col. Neal Mayo, commander of the 2nd Brigade, said during a break in training last week that a “very deliberate approach” was taken to mitigating the spread of COVID-19 with the creation of a training bubble at the remote Kahuku Training Area.

“So we obviously deployed directly from Schofield Barracks out here to the training area, and that’s where we have been for the last about 10 or 12 days now — having not interacted with anyone outside, and so we believe that that sort of bubble-type approach, which we continue to apply at every level, is helping us mitigate the spread,” Mayo said.

Soldiers in confined spaces like command tents wore masks, but in the field they didn’t if they could maintain 6 feet of separation.

“Generally speaking, we should be operating in a distributed manner anyway,” Mayo said. “I mean, that’s the tactically correct approach and so, given that approach, we should be socially distancing in an appropriate manner.”

The brigade said that as a whole it has had three positive coronavirus cases, including family members, and all were related to travel to the mainland.

Before heading into the field, the brigade tried to monitor soldier activity to minimize risk, and going into Lightning Forge “we did not have any soldiers who had coronavirus or any symptoms” that would lead to suspicion for the virus, said Maj. Panfilo Delacruz, the brigade surgeon.

As of Wednesday, 43 soldiers were “in the moderate-risk category; they exhibited symptoms that could be related to COVID” and were removed from contact, Mayo said.

Five soldiers had been tested for the virus and all had negative results, he said.

The exercise also took place at Schofield Barracks proper, East Range and Dillingham Army Airfield, with a large helicopter presence and military convoys a regular sight between Schofield and the North Shore. Artillery also was used. Only blank rounds were fired in Kahuku.

The Lightning Forge practiced over the past two weeks is a reflection of new threats in the world, meanwhile, particularly “great power” competition with China and Russia and ongoing worries about North Korea.

The exercise featured simulated enemy tanks and armored personnel carriers that soldiers battled in Kahuku — a big departure from the low-tech warfare faced in Afghanistan and Iraq, but also not representative of a fast-moving missile war that may one day come to the islands of the Western Pacific.

Other Schofield soldiers took on the role of the opposing force in Lightning Forge.

The fictitious Republic of Torbia requested help from the United States after Torbia was invaded by “special purpose” forces with the anticipation of more conventional troops arriving, Mayo said.

One of the biggest battles occurred through the night Tuesday after Schofield soldiers had taken a town and a force of about 600 was counter-attacked by three times as many enemy troops that had tanks and other armored vehicles.

“For a light infantry organization in this type of terrain, that is a hefty task,” said Lt. Col. Rick Turner, commander of the 1st Battalion, 21st Infantry Regiment.

Schofield soldiers fought back with shoulder- and Humvee-mounted missiles and other weapons and with the help of attacking Apache helicopters.

“I suspect the shift to facing a near-peer army” such as China or Russia “drove the scenario,” said Carl Schuster, a defense expert and professor at Hawaii Pacific University.

He added that, “We have been fighting terrorists for nearly 20 years and they lack tanks. China, North Korea and Russia, on the other hand, have armored mechanized forces with several thousand tanks.”

Spc. David French, 23, a weapons repairer, said he had never experienced a battle involving tanks in training, but that it was a good “curveball” for possible real-world events.

Spc. Joseph Charnley, a 20-year-old M240 machine gunner who has been in the Army about two years, said “just the size of it (the exercise), how many people they’ve got out here” was impressive.

The hardest part was the lack of sleep “staying up all night, all day, just trying to keep the body together,” he said.

“It’s been tough. It’s definitely warm out here. Takes a toll on the boys, but we’re getting through it,” Charnley said.