Jeremy McCarthy’s scientific contributions

Zygalski sheets, developed by Polish codebreaker and mathematician Henryk Zygalski in 1938, were a manual grid-based cardboard system used by the Polish Cipher Bureau and Bletchley Park to aid the decryption of German Enigma machine cipher messages. Lacking original artefacts and visual historical representation thereof, the Top Secret exhibition curator Dr Elizabeth Bruton turned to external experts on the Polish cipher bureau and codebreaking in the Second World War, Dr Dermot Turing (writer) and Jeremy McCarthy (volunteer at The National Museum of Computing (TNMOC)). The ensuing email conversation explored how the design and use of the Zygalski sheets could be reconstructed from the existing and sometimes contradictory evidence and sources. This conversation offers a rare insight into the research process and expert peer review behind an exhibition object and label. Secondly, we offer a reflection on museum practice, exploring how the resulting reconstruction was interpreted and displayed within the Top Secret exhibition alongside authentic historic artefacts from the Science Museum Group’s and GCHQ’s historic collections.