Navy sailor Lindsay Cooper knew something was wrong when billows of metallic-tasting snow began drifting over USS Ronald Reagan.

“I was standing on the flight deck, and we felt this warm gust of air, and, suddenly, it was snowing,” Cooper recalled of the day in March 2011 when she and scores of crewmates watched a sudden storm blow toward them from the tsunami-torn coast of Fukushima, Japan.

The tall 24-year-old with a winning smile didn’t know it then, but the snow was caused by the freezing Pacific air mixing with a plume of radioactive steam from the city’s shattered nuclear reactor.

Now, nearly three years after their deployment on a humanitarian mission to Japan’s ravaged coast, Cooper and scores of her fellow crew members on the aircraft carrier and a half-dozen other support ships are battling cancers, thyroid disease, uterine bleeding and other ailments.

“We joked about it: ‘Hey, it’s radioactive snow!’ ” Cooper recalled. “I took pictures and video.”

But now “my thyroid is so out of whack that I can lose 60 to 70 pounds in one month and then gain it back the next,” said Cooper, fighting tears. “My menstrual cycle lasts for six months at a time, and I cannot get pregnant. It’s ruined me.”

The fallout of those four days spent off the Fukushima coast has been tragic to many of the 5,000 sailors who were there.

At least 70 have been stricken with some form of radiation sickness, and of those, “at least half . . . are suffering from some form of cancer,” their lawyer, Paul Garner, told The Post Saturday.

“We’re seeing leukemia, testicular cancer and unremitting gynecological bleeding requiring transfusions and other intervention,” said Garner, who is representing 51 crew members suing the Tokyo Electric Power Co., which operates the Fukushima Daiichi energy plant.

“Then you have thyroid polyps, other thyroid diseases,” added Garner, who plans to file an amended lawsuit in federal court in San Diego next month that will bring the number of plaintiffs past 70.

Senior Chief Michael Sebourn, a radiation-decontamination officer, was assigned to test the aircraft carrier for radiation.

The levels were incredibly dangerous and at one point, the radiation in the air measured 300 times higher than what was considered safe, Sebourn told The Post.

The former personal trainer has suffered a series of ailments, starting with severe nosebleeds and headaches and continuing with debilitating weakness.

He says he has lost 60 percent of the power in the right side of his body and his limbs have visibly shrunk.

“I’ve had four MRIs, and I’ve been to 20 doctors,” he said. “No one can figure out what is wrong.”

He has since retired from the Navy after 17 years of service.

Even as the Reagan was steaming toward the disaster, power-company officials knew the cloud of steam they were releasing — in order to relieve pressure in the crippled plant — was toxic, the lawsuit argues, a claim that has also been made by the Japanese government.

Tokyo Electric Power also knew that radioactivity was leaking at a rate of 400 tons a day into the North Pacific, according to the lawsuit and Japanese officials.

“We were probably floating in contaminated water without knowing it for a day and a half before we got hit by that plume,” said Cooper, whose career as a third-class petty officer ended five months after the disaster for health reasons.

The toxic seawater was sucked into the ship’s desalinization system, flowing out of its faucets and showers — still radioactive — and into the crew member’s bodies.

“All I drink is water. You stay hydrated on that boat,” said Cooper, who worked up to 18 hours at a time on the flight deck loading supplies onto a steady stream of aid helicopters for four days, all the while drinking out of the two-gallon pouch of water hooked to her gear belt.

By the time the Reagan realized it was contaminated and tried to shift location, the radioactive plume had spread too far to be quickly outrun.

“We have a multimillion-dollar radiation-detection system, but . . . it takes time to be set up and activated,” Cooper said.

“And then we couldn’t go anywhere. Japan didn’t want us in port, Korea didn’t want us, Guam turned us away. We floated in the water for two and a half months,” until Thailand took them in, she said.

All the while crew members had been suffering from excruciating diarrhea.

“People were s- -tting themselves in the hallways,” Cooper recalled.

“Two weeks after that, my lymph nodes in my neck were swollen. By July, my thyroid shut down.”

Cooper, the single mother of a 4-year-old girl named Serenity, says her biggest worry is that she will get cancer. Her own mother died recently of breast cancer at age 53.

“This isn’t about financial gain,” Cooper said of the lawsuit. “This is about what’s going to happen while I’m sick, and then after I’m gone.”

“I worry,” she added, her voice choking, “because I have a daughter. And I’m so sick.”