That time physicist John Wheeler left classified H-bomb documents on a train

Jennifer Ouellette in Ars Technica:

In the popular science world, physicist John Wheeler is probably best known for popularizing the term “black hole,” although his research spanned a broad range of fields, including relativity, quantum theory, and nuclear fission. He also worked on Project Matterhorn B in the early 1950s, the controversial US effort to develop a hydrogen bomb. In January 1953, Wheeler accidentally left a highly classified document concerning that program on a train as he traveled from his Princeton, New Jersey home to Washington, DC. It was a stereotypical “absent-minded professor” moment, and one with significant national security implications.

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