U.S. Is Destroying the Last of Its Once-Vast Chemical Weapons Arsenal

In a sealed room behind a gantlet of armed guards and three rows of high barbed wire at the Army’s Pueblo Chemical Depot in Colorado, a team of robotic arms was busily disassembling some of the last of the United States’ vast and ghastly stockpile of chemical weapons.

In went artillery shells filled with deadly mustard agent that the Army had been storing for more than 70 years. The bright yellow robots pierced, drained and washed each shell, then baked it at 1,500 degrees Fahrenheit. Out came inert and harmless scrap metal, falling off a conveyor belt into an ordinary brown dumpster with a resounding clank.

“That’s the sound of a chemical weapon dying,” said Kingston Reif, who spent years pushing for disarmament outside government and is now the deputy assistant secretary of defense for threat reduction and arms control. He smiled as another shell clanked into the dumpster.

The destruction of the stockpile has taken decades, and the Army says the work is just about finished. The depot near Pueblo destroyed its last weapon in June; the remaining handful at another depot in Kentucky will be destroyed in the next few days. And when they are gone, all of the world’s publicly declared chemical weapons will have been eliminated.

The American stockpile, built up over generations, was shocking in its scale: Cluster bombs and land mines filled with nerve agent. Artillery shells that could blanket whole forests with a blistering mustard fog. Tanks full of poison that could be loaded on jets and sprayed on targets below.

They were a class of weapons deemed so inhumane that their use was condemned after World War I, but even so, the United States and other powers continued to develop and amass them. Some held deadlier versions of the chlorine and mustard agents made infamous in the trenches of the Western Front. Others held nerve agents developed later, like VX and Sarin, that are lethal even in tiny quantities.

American armed forces are not known to have used lethal chemical weapons in battle since 1918, though during the Vietnam War they used herbicides like Agent Orange that were harmful to humans.

The United States once also had a sprawling germ warfare and biological weapons program; those weapons were destroyed in the 1970s.

The United States and the Soviet Union agreed in principle in 1989 to destroy their chemical weapons stockpiles, and when the Senate ratified the Chemical Weapons Convention in 1997, the United States and other signatories committed to getting rid of chemical weapons once and for all.

But destroying them has not been easy: They were built to be fired, not disassembled. The combination of explosives and poison makes them exceptionally dangerous to handle.

Defense Department officials once projected that the job could be done in a few years at a cost of about $1.4 billion. It is now wrapping up decades behind schedule, at a cost close to $42 billion — 2,900 percent over budget.

But it’s done.

“It’s been an ordeal, that’s for sure — I wondered if I would ever see the day,” said Craig Williams, who started pushing for the safe destruction of the stockpile in 1984 when he learned that the Army was storing tons of chemical weapons five miles from his house, at the Blue Grass Army Depot near Richmond, Ky.

“We had to fight, and it took a long time, but I think we should be very proud,” he said. “This is the first time, globally, that an entire class of weapons of mass destruction will be destroyed.”

Other powers have also destroyed their declared stockpiles: Britain in 2007, India in 2009, Russia in 2017. But Pentagon officials caution that chemical weapons have not been eradicated entirely. A few nations never signed the treaty, and some that did, notably Russia, appear to have retained undeclared stocks.

Nor did the treaty end the use of chemical weapons by rogue states and terrorist groups. Forces loyal to President Bashar al-Assad of Syria used chemical weapons in the country numerous times between 2013 and 2019. According to the IHS Conflict Monitor, a London-based intelligence collection and analysis service, fighters from the Islamic State used chemical weapons at least 52 times in Iraq and Syria from 2014 to 2016.

The immense American stockpile and the decades-long effort to dispose of it are both a monument to human folly and a testament to human potential, people involved say. The job took so long in part because citizens and lawmakers insisted that the work be done without endangering surrounding communities.

Late in June at the 15,000-acre Blue Grass depot, workers carefully pulled fiberglass shipping tubes holding Sarin-filled rockets out of earth-covered concrete storage bunkers and drove them to a series of buildings for processing.

Workers inside, wearing protective suits and gloves, X-rayed the tubes to see if the warheads inside were leaking, then sent them down a conveyor to meet their doom.

It was the last time humans would ever handle the weapons. From there, robots did the rest.

Chemical munitions all share essentially the same design: a thin-walled warhead filled with liquid agent and a small explosive charge to burst it open on the battlefield, leaving a spray of small droplets, mist and vapor — the “poison gas” that soldiers have feared from the Somme to the Tigris.

For generations, the American military vowed to use chemical weapons only in response to an enemy chemical attack — and then set out to amass so many that no enemy would dare. By the 1960s the United States had a highly secret network of manufacturing plants and storage complexes around the globe.

The public knew little about how vast and deadly the stockpile had grown until a snowy spring morning in 1968, when 5,600 sheep mysteriously died on land adjacent to an Army test site in Utah.

Under pressure from Congress, military leaders acknowledged that the Army had been testing VX nearby, that it was storing chemical weapons at facilities in eight states and that it was testing them in the open air at a number of locations, including one site 25 miles from Baltimore.

Once the public learned the scope of the program, the long path to destruction began.

At first, the Army wanted to do openly what it had done secretly for years with outdated chemical munitions: load them onto obsolete ships and then scuttle the ships at sea. But the public responded with fury.

Plan B was to burn the stockpiles in huge incinerators — but that plan, too, hit a wall of opposition.

Mr. Williams was a 36-year-old Vietnam War veteran and cabinetmaker in 1984 when Army officials announced that nerve agent would be burned at the Blue Grass depot.

“There were a lot of people asking questions about what would come out of the stack, and we weren’t getting any answers,” he said.

Outraged, he and others organized opposition to the incinerators, lobbied lawmakers and brought in experts who argued that the incinerators would spew toxins.

Incinerators in Alabama, Arkansas, Oregon and Utah, and one on Johnston Atoll in the Pacific, were used to destroy a large part of the stockpile, but activists blocked them in four other states.

Following orders from Congress to find another way, the Defense Department developed new techniques to destroy chemical weapons without burning.

“We had to figure it out as we went,” said Walton Levi, a chemical engineer at the Pueblo depot, who started working in the field after college in 1987 and now plans to retire once the last round is destroyed.

At Pueblo, each shell is pierced by a robot arm, and the mustard agent inside is sucked out. The shell is washed and baked to destroy any remaining traces. The mustard agent is diluted in hot water, then broken down by bacteria in a process not unlike the one used in sewage treatment plants.

It yields a residue that is mostly ordinary table salt, Mr. Levi said, but is laced with heavy metals that require handling as hazardous waste.

“Bacteria are amazing,” Mr. Levi said as he watched shells being destroyed during the last day of operations at Pueblo. “Find the right ones, and they’ll eat just about anything.”

The process is similar at the Blue Grass depot. Liquid nerve agents drained from those warheads are mixed with water and caustic soda and then heated and stirred. The resultant liquid, called hydrolysate, is trucked to a facility outside Port Arthur, Tex., where it is incinerated.

“It’s a good piece of history to have behind us,” said Candace M. Coyle, the Army’s project manager for the Blue Grass depot. “That’s the best part about it, is that it’s not going to harm anyone.”

Irene Kornelly, the chair of the citizens’ advisory commission that has overseen the process at Pueblo for 30 years, has kept track as nearly one million mustard shells were destroyed. Now 77, she stood leaning on a cane and craned her neck to see the last one be scrapped.

“Honestly, I never thought this day would come,” she said. “The military didn’t know if they could trust the people, and the people didn’t know if they could trust the military.”

She looked around at the plant’s beige buildings and the empty concrete storage bunkers on the Colorado prairie beyond. Nearby, a crowd of workers in coveralls with emergency gas masks slung on their hips gathered to celebrate. The plant manager blasted “The Final Countdown” on the P.A. and handed out red, white and blue Bomb Pops.

Ms. Kornelly smiled as she took it all in. The process had been smooth, safe, and so plodding, she said, that many residents of the region had forgotten it was going on.

“Most people today don’t have a clue that this all happened — they never had to worry about it,” she said. She paused, then added, “And I think that’s just as well.”