Los Alamos National Laboratory

The gun-type bomb was never tested — yet it was the one they trusted. What Hiroshima's design and aftermath reveal about nuclear war.

The Manhattan Project wasn't just physicists on a mesa. It was 130,000 workers, secret cities, and an industrial effort we rarely hear about.

With the New START treaty expired, how does the US ensure its 70-year-old nuclear warheads still work without ever testing them?