In the chilly dusk on a recent Saturday, nine people were creeping through the California hills. Their faces were painted in shades of green, yellow, brown and black, so that they blended into their surroundings. Moving uphill through thickets of trees, they tried to be silent, as if not to draw the attention of some unseen enemy. They were conscious of every breath, every dry leaf that crunched underfoot, every snapped twig.

These people were not military personnel. They were just civilians — biotech workers, a masseuse, an entrepreneur — who had decided to spend a weekend preparing themselves for a war, societal collapse or some other calamity.

A booming voice broke the silence: “Camo! Five, four, three, two, one!”

The person giving the order was Jessie Krebs, a wilderness expert who has trained hundreds of U.S. Air Force officers in how to stay alive behind enemy lines through an intensive course called Survival, Evasion, Resistance and Escape, or SERE.

“Remember,” Ms. Krebs, 51, called out. “Your mission is to hide from me. You want to put objects between me and you. If you’re in the open, you don’t want to look human. You want to evade detection from the enemy.”

The nine people — who had each paid about $800 to take part in a weekend-long SERE class devised for civilians by Ms. Krebs and her colleagues at the California Survival School — went into stealth mode. A few ducked behind boulders or trees. Others hunkered low to the ground. They morphed their bodies into curious shapes.

Outdoor education programs, survival courses and military simulations have been in high demand as wars abroad intensify and prospective voters in the 2024 presidential election tell pollsters and journalists about their fears of a civil war or even World War III.

That anxiety has informed a number of recent books, including “How Civil Wars Start” by Barbara F. Walter and “The Next Civil War” by Stephen Marche. It also underlies the recent Netflix hit “Leave the World Behind,” starring Julia Roberts, which ends with images of Manhattan under attack, and “Civil War,” an A24 film scheduled to come out in April, days after Pennsylvania’s presidential primary.

The California Survival School teaches wilderness skills and stealth and evasion techniques to a few thousand people each year. Dan Baird, the owner and founder of the school, said the roots of SERE training go back to World War I. The nine who had gathered here, about an hour’s drive from San Francisco, were encountering the training for the first time.

They would not be schooled in the “RE” part of SERE — that is, resistance and escape. That would involve exposure to stimulated stressors (mental and physical) faced by prisoners of war. Those interested in gaining those skills could contact the school to request private classes, according to its website.

Before heading into the woods, the group members painted one another’s faces so that they would blend into this particular patch of wilderness. In a grove of oaks, Sarah Beth Riess, a masseuse from Mendocino County, described her reasons for signing up as Mr. Baird slathered her face in ashy clay.

“People say, Why are you taking this survival class?” Ms. Riess, 42, said. “And my question to them is, Why wouldn’t you?”

“The way the world is today,” she continued, “it seems to me it’s just logical. I’m sure it is only a matter of time before conflicts are in our faces — and not just on the news.”

Nearby, two soft-spoken brothers from Aurora, Ill., Caleb Berry, 22, and Eli Berry, 21, were scooping clay from abalone shells. “Humans are the most dangerous creatures on earth,” Eli said. “So it’s helpful to know how to evade them, if you ever need to.” He added, “The chances of actually needing these skills are very low, obviously, so it’s about having a broad skill set.”

Caleb, who said he was about to join the Marine Corps, felt the same way. “I’m not expecting anything to happen,” he said, “but if something does happen, it’s nice to have the skills.”

Others in the group included a married couple, Tina Flowers, 39, and, Parker Flowers, 42, who work in biotech in the Bay Area. They said they weren’t taking the class because they feared some disastrous event.

“Sometimes we talk about that stuff,” Mrs. Flowers said as she painted her husband’s face, “but it wasn’t the motivation to be here. But you never know, do you?”

“When we moved to California from Connecticut, we made a commitment to become more outdoorsy,” Mr. Flowers said. “The usual thing you do when you move to California.”

The couple said they were also fans of wilderness television shows, which have played a part in making survival schools popular. Ms. Krebs, the instructor, is an alumna of “Alone,” a survival competition series on the History channel.

“I can feel my stealth-and-evade mentality coming on,” Mr. Flowers said, once his face was fully painted.

That night, in the glow of their red and green headlamps, the students assembled in a clearing for dinner. On the menu was that military staple, the Meal, Ready-to-Eat, or M.R.E. It included chili, beef strips, applesauce, Skittles and hot cocoa.

Ms. Krebs pointed out the Cassiopeia constellation. A jocular conversation among the attendees turned more serious when it touched on artificial intelligence.

“I have enough knowledge as far as tech goes to know that A.I. is scary,” said Lawrence Yu, a 44-year-old tech entrepreneur from Berkeley. “Essentially, we will have something that will be catastrophic for the human race. I put the probability at 50 percent in the next 10 years.”

When asked if the rise of A.I. was a reason he had signed up for the SERE course, he was quick to answer: “Absolutely zero. There is no way you could ever evade it, dude. Thermal detection, night vision. If something like that gets out of control, I don’t want to be here.”

“I am worried about urban stuff in America,” he continued. “There’s strife around ideologies already, call it ‘woke’ and conservative. I’m bracing myself for more fires around that. Here and abroad, these are interesting times. It’s rocky roads.”

Mr. Yu said his interest in survivalism germinated after reading “Emergency,” a 2009 book by Neil Strauss on his transformation from “helpless urbanite” to independent survivalist. “The coolest thing to do is to develop a skill set like James Bond,” Mr. Yu said. Of late, he said, he had taken up flying lessons, despite a fear of heights; learned to pick locks; and fired guns. Would he take more courses after this one? “Yes, absolutely,” he said.

Night fell. Ms. Krebs told the crew to set up sleeping arrangements as inconspicuously as possible. They rigged a camouflaged tarp in near silence. Sleep came easily for some. Others struggled. Curious horses entered the encampment, amusing some of the students and terrifying others (including this reporter).

At dawn, the participants scraped the underbrush to remove all traces of their presence. Olivia Garrido, 29, was tending to her patch between two fallen branches. A self-employed restaurant equipment repairs and liquidations worker who lives in Utah, she said she saw the merit in the SERE course.

“The evasion stuff for me is interesting,” she said. “It’s a sad reality, but as a woman, I’m happy to learn it, because I do a lot of solo hikes. On those trails, it’s good to be able to evade and avoid certain people.”

Ms. Garrido added that she looked forward to using her new skills on trips to national parks, mostly to witness nature undisturbed: “I love the desert, and I’d like to take some of these lessons so that, when I go there, I can muffle my presence and be able to witness wildlife up close.”

In the midmorning light, the group descended to base camp. Jorge Merlos, a 30-year-old animal caretaker at a wolf sanctuary, used point-to-point compass navigation as he maneuvered through the wilderness and communicated with his course partner, Ms. Garrido, with hand and eye gestures.

“When I have a family,” Mr. Merlos said, “I want them to trust me as a source of knowledge and protection, especially if we’re in the wilderness.” Asked if his interest in SERE had anything to do with the tense national mood, he said, “There is a saying: ‘It is better to be a warrior in a garden than a gardener in a war.’”

Toward the end of the day, the group went over general survival skills — how to stay alive and mentally healthy while alone in the wilderness. Then the rain came down, and the hill country became a soggy mess.

“Rain,” Ms. Krebs said. “It’s actually pretty good for evasion.”

Huddled under a tarp, she delivered her final lesson, on strategies for surviving nuclear and biological attacks. Later, she explained a little about her worldview and her thoughts on teaching SERE.

“There are many legitimate reasons why you may want to seek out this type of thing,” she said. “There are tactical, scary reasons, but many others, too, and sometimes it’s just fun. The key question I ask people who come here, though, is, Do you think the world is kind? If you answer yes, then I want to teach you. If it’s a no, I’m not as interested, because that’s operating from paranoia and fear.”

“We get a fair few of those mind-sets in SERE courses,” she continued. “I personally believe in a friendly universe, and I hope that comes across when I teach.”

At the end of the course, the nine students posed for group photos, shook hands and hugged. As the rain continued, they got into their cars — sedans, S.U.V.s, pickup trucks — and drove past a field of oats, back to their everyday lives.