William Shuttleworth embarks Wednesday on one of his biggest adventures yet: A 3,000-mile walk across the U.S.

The slim, fit 71-year-old Air Force veteran will set out on a 7-month walk from his hometown of Newburyport, Massachusetts, to Vandenberg Air Force Base in California, with the goal of drawing attention to the plight of homeless veterans.

According to the Department of Housing and Urban Development, in 2018 there were nearly 39,000 vets experiencing homelessness on any given night in the U.S., including 985 in Massachusetts. Shuttleworth says he hopes to meet with veterans in small groups and individually along his walking route. Via his website, he aims to raise awareness of the problem and money for the Disabled American Veterans Association.

“I've been walking 20 miles to 25 miles every day, just because I enjoy it, since I've been retired, “ Shuttleworth said in an inteview with WGBH News a few days before starting his journey. “And since I walk 20 miles every day, why not make that a straight shot across the country, and engage people in conversations that have a real meaningful purpose.”

Shuttleworth will set off first from a Newburyport café, just a stone’s throw from his house. From there, he will walk four and a half hours west to Haverhill.

“And then I head toward Route 2 and go all the way to Williamstown, into New York, through Troy, ... go across the state of New York and into Pennsylvania, on into Ohio, Indiana, Illinois, Missouri, Kansas, Colorado, Utah, Nevada and then California," he said.

During the Vietnam War, Shuttleworth worked as an Air Force psychologist, primarily with former prisoners of war. In the past few decades, he served as superintendent in public school districts throughout Maine. Last year, Shuttleworth and his wife Patty managed a campground in California, where they often allowed vets to stay for free.

Shuttleworth said it was sitting down with these vets and talking to them that sparked the idea for his trek to California.

“What I would try to do is gather food and wood so that they'd have a place to stay and they'd be safe and protected and supported and loved," he said. "We had regular visitors, and sometimes they'd get hooked on opioids and other drugs. They have a lot of PTSD, a lot of mental issues.”

Andrew McCawley, president and CEO of the New England Center and Home for Veterans in downtown Boston, said he is awed by Shuttleworth’s journey.

“It's admirable that this gentleman would do this, and I think the most important thing that would could come from his personal journey across this country is a sense of awareness,” McCawley said.

He added that he is excited that Shuttleworth is calling attention to the issue of veterans’ homelessness — a problem that peaked in 2011.

“Although veterans still experience homelessness, no longer are they necessarily experiencing at a higher rate than the general population. But it does remind us that our work is not done," McCawley said.

Prior to setting out on his journey, Shuttleworth had pared his supplies — including a portable stove, walking sticks, backpack and sleeping bag — down to only 24 pounds.

Shuttleworth said he is well aware of the obstacles he is likely to encounter on this trip, especially as Kansas gives way to Colorado and the end of the great plains. He's especially concerned about having to get over the Rockies, and then through — or around — Death Valley, CA.

And then there are the people he might encounter, which Patty said she is somewhat concerned about.

“We live in a world that while many people are very, very helpful and pleasant, there are unpleasant people and things that could happen. But we're optimistic and he has a great way with people,” she said.

Shuttleworth has also been told by his doctor that his body, his cartilage and his legs may not do well on the 3,000-mile walk. But Shuttleworth said he’s fired up by something much more powerful than the physical demands of the journey.

"If you lived every day with everything that could go wrong, a person would never get out of bed," he said. "I embrace this as a gift to myself and hopefully as a gift to the people that need it most."

Correction: An earlier version of this story incorrectly stated that Shuttleworth began his trip on Tuesday. He starts his journey on Wednesday, May 15.