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. And then some of the guys fainted. And finally they opened the door and let us out, and the...