CIRCA 1944

Unlike the better known ENIGMA cipher machine, the Schluesselgeraet 41 (SG-41) remained a secure cipher device, unsolved by the cryptanalysts at Bletchley Park. Fortunately for the Allies, such machines were introduced too late and in too few numbers to make a difference to the outcome of the war; a now declassified report in 1946 by the American Security Agency states that 11,000 machines were ordered but "only a small (unknown) quantity had been manufactured and put in use" (vol 2. Notes on German high level cryptography and cryptanalysis, available online). Two versions are known, one with an alphanumeric keyboard, and the present example with numeric keyboard that was used for weather service communications by the Luftwaffe. Due to the small number produced, the SG-41 remains much rarer than the ENIGMA to this day.

Based on a similar design to the cipher machines invented by Boris Hagelin (1892-1983), the SG-41 employed interacting irregular wheel motions. Not having an electric core, it was powered by a hand-crank, but the heavy metal frame must have made it cumbersome to carry. According to the 1946 report it suffered from mechanical faults, that could have been corrected by improved engineering - probably explaining why it didn't see earlier and wider use.