The U.S. government confirmed for the first time that it grouped American troops by race when testing mustard gas and other chemical agents during World War II, while using white soldiers as a control group against others. The program remained classified until 1993, and participants were not given follow-up medical care. Japanese-American and Puerto Rican soldiers were also tested. “They said we were being tested to see what effect these gases would have on black skins,” one former soldier told NPR. NPR reports that the government has not yet provided records that would show the motivations behind such experiments.