As a young U.S. Army soldier during World War II, Rollins Edwards knew better than to refuse an assignment. When officers led him and a dozen others into a wooden gas chamber and locked the door, he didn't complain. None of them did. Then, a mixture of mustard gas and a similar agent called lewisite was piped inside. It felt like you were on fire," recalls Edwards, now 93 years old. "Guys started screaming and hollering and trying to break out." Edwards was one of 60,000 enlisted men enrolled in a once-secret government program – formally declassified in 1993 – to test mustard gas and other chemical agents on American troops. But there was a specific reason he was chosen: Edwards is African-American. While the Pentagon admitted decades ago that it used American troops as test subjects in experiments with mustard gas, until now, officials have never spoken about the tests that grouped subjects by race. All of the World War II experiments with mustard gas were done in secret. [Subjects] received no follow-up health care or monitoring of any kind. They were sworn to secrecy about the tests under threat of dishonorable discharge and military prison time. In 1991, federal officials for the first time admitted that the military conducted mustard gas experiments on enlisted men during World War II. However the race-based experiments remained largely a secret until ... 2008. Despite months of federal records requests, NPR still hasn't been given access to hundreds of pages of documents related to the experiments, which could provide confirmation of the motivations behind them.