As he stepped off a small jet into the Massachusetts snow on Saturday morning, Army Chief of Staff General James McConville raised his elbow to give air bumps to members of the state National Guard who were there to greet him.

The most senior officer in the Army, McConville has been in war zones around the world. Now, the Bay State native is fighting a different kind of war — and this time, the battleground is at home.

“What’s different about this is that it’s a fight against an invisible enemy,” McConville said at a press conference with Mass. Gov. Charlie Baker on Saturday. "We remain Army strong, Massachusetts strong, and Boston strong. This is a great state, and we will defeat this virus."

The general looked down for a moment.

“I was born and raised in Quincy," he continued. "My dad still lives in the house we grew up in. I have tremendous pride being from the Boston area, and we’re just very thankful to have the opportunity to get back to the community and work with all the great professionals here trying to defeat the virus.”

As the COVID-19 pandemic morphed into a national crisis, the military has been instrumental in enabling states to expand their medical capacity — particularly those that were hit hardest, like Massachusetts and New York.

The Army Corps of Engineers has helped build field hospitals like "Boston Hope," the 1,000-bed field hospital set up inside the Boston Convention and Exhibition Center, where McConville and Baker spoke on Saturday. And Army reserve medical units are deploying to help treat patients with coronavirus across the state.

“The military’s job is to protect the nation," McConville said. "We have a threat right now, and that’s why we’re here to assist communities like Massachusetts and Boston."

The state has been taking its own actions to fight the spread of COVID-19, including building field hospitals, implementing stay-at-home orders and ramping up testing. But the pandemic has grown at a scale that threatened to outpace the local response. At the press conference on Saturday, Gov. Baker said that while the state is meeting or exceeding its goals for testing, Massachusetts is still nowhere near where it needs to be.

“What’s the right number of testing? I’m not sure," he said. "I just know it’s a lot more than we’re doing now, even though we’re one of the biggest testers at a per capita basis in the country right now."

That’s where the Army can help, a senior Army officer and spokesman said: by quickly scaling up the size and speed of the response. For instance, with help from the Corps of Engineers, the Boston Hope field hospital was finished less than a week after preparations began. Army medical reserve units are now treating patients in the Seaport convention center, and will soon be supplementing medical staff at other facilities in the state.

“These are reserve soldiers. They normally serve in a combat surgical hospital,” McConville said. “They’re working side by side with commonwealth partners to take care of COVID patients."

The Army activated roughly 1,500 members of the National Guard in Massachusetts, many of whom are running mobile coronavirus testing labs at sites around the state. That includes the Soldiers’ Home in Holyoke, where the virus swept aggressively through residents and staff. As of April 17, at least 48 residents at the home have died due to COVID-19, and another 91 have tested positive.

McConville said Army medical research labs are also working with Massachusetts researchers at Beth Israel Deaconess Medical Center and the Broad Institute to develop a COVID-19 vaccine and other medical treatments.