Kathleen Ehl had always thought of her business as a niche affair — an online store called North Georgia Outdoors Supply that she and her husband run out of their home in Gainesville, selling Meals, Ready to Eat.

M.R.E.s, as they widely known, are thick pouches of shelf-stable rations created for the United States military. They’re not particularly fancy or appetizing, and they’re technically not allowed to be sold commercially if they are made under a government contract, as most are. Ms. Ehl and her husband, Oliver Walker, scour online auctions and salvage stores for the meals, and sell most of them to collectors and survivalists.

But last February, when pandemic-induced panic buying kicked into high gear, their orders jumped from 100 a week to 100 a day. “There were some nights my husband and I packed M.R.E.s from after the kids went to bed to 2 in the morning,” said Ms. Ehl, 37.

Early 2020 was a boom time for M.R.E. distributors across the country, from the major military suppliers to Army surplus stores. Yet today, as purchases of other pandemic fixations have flagged, the civilian fascination with the meals has persisted — driven by caution (stocking up for the next potential pandemic or natural disaster) and curiosity.

Though sales figures for M.R.E.s are hard to come by, given the questionable legality of some sales, the internet audience that discusses and taste-tests the rations has grown to millions. People who never thought they’d own an M.R.E. now keep them in their basement.

Sylvia Marie, 26, ordered a few, including a Mexican-style chicken stew and a vegetarian taco pasta, shortly into the lockdown, while staying at her relatives’ home in South Windsor, Conn. She was looking for foods that were new to her and didn’t require a great effort to make.

On the website where she placed her order, “a lot of the reviews were people who had been talking about how they had bought these to stock their bomb shelters,” said Ms. Marie, a food-policy researcher at Tufts University. “I don’t think I would normally associate myself with that population.”

No one is more intrigued or puzzled by the phenomenon than the scientists and engineers who research and develop the meals at the Department of Defense Combat Feeding Division. At the division’s headquarters in Natick, Mass., the team spends years perfecting every detail of an M.R.E. before it is sent off to manufacturers: Is this beef ravioli as nutritious as possible, and shelf stable for up to three years? Can it survive a drop from a helicopter, or blistering desert temperatures?

M.R.E.s are explicitly made for service members on operations away from a dining hall or field kitchen. Yet many people outside the military have long been interested in what soldiers eat. Wartime museums display the bland hardtack that sustained Civil War fighters, and the canned meats, breads and fruit of World War II, known as C rations.

In the 1990s, after complaints from soldiers serving in the Persian Gulf war, the focus of ration development shifted to creating better-tasting and more diverse meals. Service members were invited to submit ideas for the menu, which expanded to 24 entrees, from 12, with vegetarian, halal and kosher options available.

Every year, the least popular M.R.E.s are dropped from circulation and new ones are added; perennial favorites like spaghetti with meat sauce or beef ravioli are supplemented with dishes like a Mexican rice and bean bowl. In 2018, the highly anticipated pizza M.R.E. was introduced, made possible by technology that creates barriers to micro-organism growth between the layers of sauce, cheese and bread.

Each M.R.E. contains a complete meal — an entree, snacks, dessert and beverages — with an average of about 1,200 calories and a variety of vitamins and minerals, some of them added. Every ingredient is meant to serve a purpose — the beef jerky is fortified with caffeine, and the applesauce contains maltodextrin, which provides an energy boost.

These food choices play a critical role on the battlefield, said Stephen Moody, the Combat Feeding Division chief. “The right nutrition might be able to give us an edge,” increasing a soldier’s alertness or decision-making capabilities, he said.

But why would a civilian want to eat one?

“I don’t know,” said Julie Smith, a food technologist in the division. The new interest, she added, seems antithetical to the growing movement toward buying fresh produce and cooking from scratch.

Some veterans are just as bewildered. “It cracks me up,” said Emmanuella Franco, 27, who was a specialist in the Army National Guard from 2013 to 2019 and now works as a microbiology technician in Keeno, Calif. “You want to eat this nonmelting piece of plastic? That’s on you, man.”

Despising M.R.E.s is a long tradition in the military, where they have earned nicknames like “Meals, Rejected by Everyone” or “Meals, Rarely Edible.”

But on platforms like YouTube and TikTok, a growing cadre of M.R.E. taste testers (most of them nonmilitary) are transfixed. They open and examine each component, including snacks like the ever-sought-out jalapeño cheese spread and popular desserts like cherry blueberry cobbler, as well as an accessory packet that usually contains toilet paper, a moist towelette, chewing gum and salt. Older M.R.E.s may include cigarettes, while non-American ones might have alcoholic drinks.

One of the best-known YouTube reviewers is Steven Thomas. The 1.8 million subscribers to his channel Steve1989MREInfo have watched him fearlessly and even enthusiastically eat canned pork and eggs dating to 1945, or a ham and chicken loaf from 1984. Last April, views of his videos spiked to nine million, an all-time high for his channel.

After first trying an M.R.E. at age 8 — his father bought him one from an Army supply store in Lakewood, Fla., where Mr. Thomas still lives — he became obsessed with tracking down rations from various countries and eras. In 2015, he started tasting them on camera.

The rations are “the closest thing to time travel,” said Mr. Thomas, 32. “When you open something, and air hasn’t touched that stuff in 50 or 100 years and it is just the same as it ever was, it is amazing.”

Even YouTube hosts with a broader scope are running M.R.E. taste tests — like Emmy Cho, who runs a popular food channel called EmmyMade. Ms. Cho, 43, said the meals are both nostalgic and surprising — you don’t always know what you’re going to find in one.

“You can look at the details of an M.R.E.” and wonder why certain foods were included, she said. It’s an accessible way to understand the military experience, which to civilians can feel like another world.

Especially during the pandemic, buying the rations has helped people “deal with a chaotic and unpredictable world,” said Anastacia Marx de Salcedo, the author of the 2015 book “Combat-Ready Kitchen: How the U. S. Military Shapes the Way You Eat.” “They are comfort food for courage.”

Development of the modern M.R.E. began in 1970, during the Vietnam War. Today’s versions contain two important innovations: the retort pouch, made of flexible materials that can withstand the heat of sterilization, providing the shelf stability of canned food without the bulkiness; and the flameless ration heater, which uses a chemical reaction to warm an entree with just a little water.

The Combat Feeding Division is constantly experimenting with ways to improve nutrition. The Massachusetts center has a food laboratory that could be mistaken for any commercial kitchen — if not for the boxes of truffle macaroni and cheese in a tube (for U.S. Air Force pilots) and the portraits of soldiers lining the walls.

On a recent Wednesday, Ann Barrett, a chemical engineer, and Michelle Richardson, a food technologist, were making vegetable omelets of varying volumes and fat content to see how a soldier could be most sated from the smallest package.

Lauren Oleksyk, who leads the food engineering and analysis team, speculated about having soldiers wear sensors that detect what nutrients they need, and having a 3-D printer generate nutritionally appropriate food to be delivered via drone. Tom Yang, another food technologist, was experimenting with what is essentially a giant microwave to turn entrees like macaroni and cheese and buffalo chicken into granola-bar-size meals that could fit in a pocket.

“We understand it’s not gourmet food,” said David Accetta, the chief of public affairs for the Army’s research and development organization that oversees rations.

True enough. In the pepperoni pizza, the crust is dense, the cheese is dry and flavorless, and the pepperoni lacks crunch and richness — yet it invokes the pleasing nostalgia of a Lunchables. The cherry blueberry cobbler is a mildly flavorful goo. The cheese tortellini are rubbery and clumpy, though well sauced. Warming an M.R.E. doesn’t fill the room with inviting aromas — all you’ll smell is the metallic odor of the magnesium and iron inside the heater.

Then again, consider the sheer number of requirements the meal has to meet, or the dire conditions in which a soldier is often eating one.

“Nasty or not, it will keep you alive,” said Joe Guerrero, 20, an Army motor transportation operator stationed in Fort Bliss, Texas.

Many M.R.E. sellers are hoping to capitalize on this spike in awareness to get civilians to think of the rations beyond the military context, and associate them with camping, hiking or emergency situations.

Blair Calder, the owner of Meal Kit Supply in Buffalo, buys M.R.E. components and repackages them in his own retort pouches — a common means of working around the commercial-resale ban. To make them more appealing to civilians, he doesn’t use the Army Stamp font or any battlefield language or imagery.

Tom Miller, a business director at Wornick Foods in Cincinnati, one of the three manufacturers that make most of the M.R.E.s, said his company is increasingly focused on manufacturing for food banks and other humanitarian organizations that help during natural disasters. (The Federal Emergency Management Agency also maintains a stockpile of the meals.)

When a storm left millions of Texans without water or electricity in February, Shoshana Krieger and Mincho Jacob, who work for the housing nonprofit Basta, said the rations were far easier than hot meals to load and transport in bulk to individuals in need. If climate change continues to amplify the impact of natural disasters, these needs may increase.

Still, M.R.E.s are far from mainstream. Selling them sometimes requires operating in a legal gray area. Ms. Ehl, of North Georgia Outdoors Supply, said she had heard of sellers’ stealing from military bases.

“There is too much of a stigma around the actual M.R.E. itself,” said Steven Cyros, the founder of M.R.E. Depot and M.R.E. Wholesalers in San Clemente, Calif., and Tucson, Ariz. And “dollars to calories, it is an expensive option” compared with other prepared foods. (A single M.R.E. typically retails for about $10.) Mr. Cyros has had little success advertising in outdoor magazines — the rations are probably too heavy for hikers, he said.

But people may already be eating in military fashion without realizing it. Many everyday foods — from Spam to energy bars — originated as rations. Even the retort pouches made for M.R.E.s are now used to package baby food and tuna.

“The military comes up with these innovations,” Ms. Marx de Salcedo said. “And when they are provided to soldiers, they seem like an odd sort of food.”

But eventually, she said, they become American comforts.

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