"The Weapon" is a science fiction short story by American writer Isaac Asimov.
Written in September 1938 when Asimov was 18, it was first published in the May 1942 issue of Super Science Stories under a pseudonym, H.B.
However, while writing the first volume of his autobiography, In Memory Yet Green (1979), Asimov came across an entry in his diary which reminded him that the story had indeed been published.
Obtaining a copy of the relevant magazine, he ensured that the story was published in chapter 30 of that book.
He infiltrates a laboratory on Deimos and, after a long search, eventually finds the information he needs, but at the moment of discovery he himself is discovered by the Martians.