Spectral lines: The automatic factory

Somewhere in the recesses of a mountain chain (the Urals?), buried hundreds of feet beneath the surface, so the story goes, is a truly automatic factory. It has no workers. It runs day and night producing a vital high-technology product - perhaps a missile part. One imagines that visiting it would be like visiting Jack Benny's money vault, except that no watchman, such as the one employed by Mr. Benny, controls the entry: one enters using a coded plastic card.