Géraud-Stewart, RémiNaccache, DavidWaldispühl, MichelleMegyesi, Beáta2024-05-082024-05-0820241736-6305https://hdl.handle.net/10062/98472https://doi.org/10.58009/aere-perennius0097“Can not find any info on Delastelle— Nothing on record in this country.” (William Friedman, 18 Jan 1955, NSA Archives A63734) Following these words, the then-director of the US National Security Agency hailed contacts in Europe, hoping that someone would fill in this missing information. The initial inquiry was sent to Friedman by amateur American cryptographer William Maxwell Bowers; in 1963, Bowers would publish under a pseudonym all that he could find on the matter (The Cryptogram 1963, preserved under reference VF 54-30 at the US National Cryptologic Museum). Since this document, which had a very limited audience, almost no new information on Delastelle was published, and indeed most of the information available widely today on Delastelle is at best fragmentary. In this paper we reopen that case, reviewing information about the life and work of Félix-Marie Delastelle, establishing data overlooked by earlier historians, correcting several oft-repeated errors and bringing novel documents to public awareness.enAttribution-NonCommercial-NoDerivatives 4.0 InternationalDelastelleFelix-Marie DelastelleHistoryBifid cipherTrifid cipherHistorical cryptographyArticle