In 1967, fire ravaged the USS Forrestal stationed off the coast of North Vietnam, killing 134 sailors. The aircraft carrier's firefighting systems had proven woefully inadequate.

The disaster prompted action. The Navy rolled out a new and far more effective fire suppressant it had been developing with 3M. By the early 1970s, the Air Force had also adopted the new firefighting foam, known as AFFF.

Sales of the foam boomed, and Maplewood-based 3M dominated the market.

But the miracle firefighting foam's key ingredient was one of the "forever chemicals" that have come to haunt 3M. PFAS chemicals don't biodegrade, tainting the environment. They have been linked to cancer, liver damage, decreased fertility and other maladies.

Today, drinking water near hundreds of military bases nationwide — where firefighting foam was primarily used in training exercises — may be contaminated with PFAS. The clean-up will cost taxpayers billions of dollars.

"The military is only in the very early stages of cleaning up these sites," said Melanie Benesh, government affairs vice president for the Environmental Working Group, a PFAS watchdog.

3M faces a flood of lawsuits — and potentially tens of billions of dollars in liabilities — over myriad consumer and industrial products that contained PFAS. But no single case is more significant in terms of size, combined with possible damages, than the firefighting foam litigation looming in South Carolina.

It pits 3,019 plaintiffs — ranging from municipal water authorities to firefighters who used AFFF — against 3M and several other firefighting foam manufacturers.

Bellwether trials are slated to start next spring, and one of the first will be a suit against 3M and other foam makers by the city of Sioux Falls, S.D. Sioux Falls was once home to an Army air base.

The firefighting foam case against 3M is akin to several PFAS lawsuits filed in the past few years. It claims the company knew of the chemicals' risks for years yet did not fully disclose them to government regulators.

But the firefighting foam litigation comes with a twist, due to the military's involvement.

3M and other AFFF makers are trying to invoke the government contractor defense. It's a powerful legal tool that shields contractors from liability for defects in products they developed and manufactured for the federal government.

3M says not only did the military help develop AFFF, it had ample information on its environmental risks and kept using it.

However, the federal judge in Charleston, S.C., presiding over the foam litigation recently dealt 3M a blow.

Judge Richard Gergel ruled Sept. 16 that foam manufacturers can use the government contractor's defense at upcoming jury trials — but he denied them an outright, blanket use of the defense.

3M and other AFFF manufacturers "had significantly greater knowledge than the government about the properties and risks associated with their products and knowingly withheld highly material information from the government," Gergel ruled.

3M said it was "disappointed" with the decision, but noted Gergel was ruling against a motion for "summary judgment." In that type of proceeding, courts are required to examine facts in a light most favorable to plaintiffs.

"We believe that the evidence at trial will demonstrate 3M met the criteria for the government contractor defense," the company said.

3M stopped making firefighting foam around 2000 because of potential environmental risks. The company stands by its handling of PFAS, arguing that the chemicals are safe to humans in the levels that exist in the environment.

While Minnesota is not a home to major military bases, the Department of Defense has been investigating PFAS contamination at Air National Guard sites in Duluth and the Twin Cities.

Large Air Force bases in Ellsworth, S.D., and Minot, N.D., are among the 50 most PFAS-contaminated U.S. military sites, according to the Environmental Working Group. The Air Force supplies drinking water to people who live near Ellsworth and several other bases.

The military is not on trial, but its actions, or lack thereof, will be scrutinized along with 3M's. The Navy and the Air Force kept tapping their 3M foam inventory for many years after 3M stopped making the product, court records show.

Also, the military did its own studies on the environmental impacts of firefighting foam, Benesh noted. "I think both 3M and the military should be held accountable," she said.

New breed of chemicals

The story behind the firefighting foam in question goes back to 1961 when Richard Tuve, a chemist at the Naval Research Lab, came across a 3M advertisement in a trade journal.

Tuve was trying to develop a better foam for fighting petroleum fires, always a danger on ships. At the time, the Navy used "protein foam," a foul-smelling concoction made from hoofs, horns and other animal detritus.

Tuve tried all sorts of chemical combinations that didn't work. 3M's ad trumpeted a new breed of chemicals made by electrochemically combining fluorine and carbon atoms into a super strong bond.

Tuve and 3M both saw the potential for fighting fires. A fluorocarbon-based film would blanket an oil fire, smothering flames, keeping vapors from igniting and fireproofing unburned fuel.

The suppressant was dubbed "aqueous film forming foam" — AFFF for short. It extinguished fires much faster than protein suppressants, and could be stored more easily aboard ships.

By 1967, the Navy was rolling out AFFF at some bases. Then came the Forrestal catastrophe in the Gulf of Tonkin off Vietnam. A rocket on an F-4 Phantom jet was inadvertently launched across the aircraft carrier's deck, sparking explosions and fires — still one of the worst Navy disasters since World War II.

"The major lessons learned [from the Forrestal] were to convert to AFFF as soon as possible," Robert Darwin, a former Naval fire protection officer, wrote in a 2005 study.

The Air Force rolled out AFFF in the early 1970s, as did other military branches.

"AFFF has helped save countless service member and civilian lives due to its unique capabilities to fight dangerous fires," 3M said in a statement. "To this day, the only product that meets the military specification governing firefighting foam is PFAS-based AFFF."

Clues in nation's blood banks

In the mid 1970s, 3M started taking a closer look at the biodegradability of its fluorochemicals — the foundation for a host of consumer products from nonstick pans to water-repellant shoes and industrial products like firefighting foam.

The inquiry began after Warren Guy, a scientist at the University of Florida, called 3M in 1975 about his research findings. Guy and toxicologist Donald Taves had discovered a fluorine chemical in samples from blood banks across the country.

They wanted to know how it got there, and suspected it might have originated from 3M's Scotchgard fabric protection products.

By 1976, 3M scientists concluded that Guy's and Taves' discovery reflected the presence of PFOS, a fluorochemical and type of PFAS exclusively manufactured in the U.S. by 3M and a key ingredient in firefighting foam and other products, a court document shows.

3M told no one of this finding for nearly a quarter of a century, Gergel wrote.

The company's lawyers "urged" its scientists not to release information on the "true identity" of the PFOS compound Guy and Taves had found, Gergel wrote, citing an internal company document.

Also, a 3M scientist published an article stating that what Guy and Taves had found was not human-made, but a naturally occurring substance.

"A reasonable inference from 3M's conduct surrounding the Guy and Taves study is that the company knowingly withheld highly significant information that PFOS was now in the blood of the general population and actively sought to discredit an independent scientific work that could have disclosed this," Gergel wrote.

3M disagreed with that characterization, and said it worked with Guy and Taves on their research.

In the wake of Guy's and Taves' findings, 3M conducted a phalanx of studies, including toxicology research on lab animals and analyses of its own workers' blood.

By 1983, the company concluded that while the chemicals didn't harm the environment or human health, they were extremely persistent and therefore could alarm regulators, court documents show.

Still, Gergel wrote that 3M represented PFOS as biodegradable, noting a 1988 internal company memo.

In the memo, a 3M environmental scientist wrote that he did not think it was in "3M's long-term interest to perpetuate the myth that these fluorochemical surfactants are biodegradable." (Surfactants reduce surface tension of a liquid).

"It is probable that this misconception will eventually be discovered, and when that happens, 3M will likely be embarrassed, and we and our customers may be fined and forced to immediately withdraw our products from the market," according to the document included in court filings.

3M said that the military was aware by the 1970s that fluorochemical surfactants were not biodegradable.

In 2000, 3M and the U.S. Environmental Protection Agency (EPA) jointly announced the company was voluntarily discontinuing PFOS production. The EPA noted the chemical's "strong tendency" to accumulate in human and animal tissue, calling it a potential risk to human health and the environment over the long term.

The announcement came two years after "3M began making long overdue disclosures to the EPA," Gergel wrote. The company had notified the agency in 1998 that it had detected PFOS in blood bank samples.

In that same year, 3M's corporate toxicology manager called PFOS-based chemistry "insidiously toxic" in an internal document, court records show. The scientist's observation was not reported to the EPA, Gergel wrote.

'Emerging risk alert'

3M's discontinuation of its firefighting foam shook the military.

"Firefighters were panicked the EPA would ban AFFF," Curtis Bowling, an assistant deputy undersecretary for the Defense Department, said in a court filing. There was no viable alternative.

But the EPA didn't ban AFFF, so the armed forces kept using 3M's product; they had a lot of it in inventory.

In 2004, the military had 2.8 million gallons of AFFF on hand, most of it held by the Air Force and the Navy, according to a study by Darwin. At the time, three-fourths of the Navy and the Air Force's AFFF came from 3M.

By 2011, the two military branches had consumed 47% of the 3M inventory they had held in 2004, the study shows.

In 2011, the Defense Department's Chemical & Material Risk Management Directorate put out an "emerging risk alert" for firefighting foam

The alert noted that the military had used unlined earthen pits at its bases to train firefighters for oil fires. Petroleum was dumped into the pits, ignited and extinguished.

The practice "may have resulted in soil and water contamination," the risk alert said.

AFFF containing PFOS remained in military inventories — and in use — until 2016, according to a 2021 report by the inspector general for the U.S. Department of Defense. The military was waiting on environmental regulators for guidance, the report said.

In May 2016, the EPA issued its first drinking water health advisories for PFOS and PFOA, another toxic PFAS chemical. The military then began addressing drinking water issues. In 2016, the Defense Department required the replacement of older, PFAS-laced AFFF.

In a statement, the Air Force said the last of its 3M AFFF inventory was removed in 2017. The Navy said it has removed all "legacy" AFFF at its U.S. facilities, and will do the same overseas by the end of 2022.

Both the Navy and the Air Force said the AFFF they use now has only trace PFAS chemicals, and that they are working on new fluorochemical-free foam.

The military's ongoing use of AFFF is critical to 3M's argument that it should be shielded by the government contractor's defense. The defense requires that contractors warn the government of any product defects.

3M argues that the military knew of potential environmental risks going back to the 1970s; the Navy and Air Force had conducted several studies on the matter. And after 3M exited the AFFF market — essentially a warning — the military didn't stop using its product.

Still, Gergel raised questions about whether 3M had adequately warned the government.

"3M could not demonstrate ... that the government's continued use was with full knowledge of the product's defects, and risks," he wrote. "Further, there are material factual disputes concerning whether 3M's belated disclosures constituted a failure of its duty to warn."