NPR investigation has uncovered a disturbing aspect of the secret chemical experiments conducted during World War II: the test subjects were chosen by race.

Although documents about the experiments were declassified in 1993, only recently has the racial component been talked about. NPR’s investigation found that not only African-Americans but Japanese Americans and Puerto Ricans were singled out for testing, with whites being used as “normal” groups for control.

Rollins Edwards, who is African-American, recalled the experience of being led into a wooden gas chamber and locked inside when mustard gas and other agents were pumped in. “It felt like you were on fire,” the 93-year-old remembered. “Guys started screaming and hollering and trying to break out. And then some of the guys fainted. And finally they opened the door and let us out, and the guys were just, they were in bad shape.”

Edwards’ experience was one of surprisingly many, though the military conducted three kinds of experiments with mustard gas. There were patch tests, in which mustard gas was applied directly to the skin; field tests, in which subjects were subjected to the gas outdoors during combat simulations; and chamber tests, like the one Edwards described.

Army Col. Steve Warren, director of press operations at the Pentagon, openly admitted to the military’s past mistakes when the NPR’s findings were shown to him. “The first thing to be very clear about is that the Department of Defense does not conduct chemical weapons testing any longer,” he said. “And I think we have probably come as far as any institution in America on race. … So I think particularly for us in uniform, to hear and see something like this, it’s stark. It’s even a little bit jarring.”

The investigation into the racial component of these tests began when Susan Smith published findings that suggested the military was looking for an “ideal chemical soldier” while testing black and Puerto Rican troops. The goal was to find soldiers who could withstand chemical attacks on the front lines while whites stayed protected in the back.

While some who were subjected to the program have now spoken about their experiences, others have remained quiet, some out of duty and others out of a wish to put the past behind them. At the time, the soldiers who participated in the experiments were told not to disclose what had been done and threatened with dishonorable discharge. Others, such as Susan Matsumoto’s husband, Tom, believed their participation would “prove he was a good United States citizen.”

“He always loved his country,” Matsumoto sid. “He said, ‘Where else can you find this kind of place where you have all this freedom?'”