A rare German Enigma enciphering machine will go under the hammer later this month.
Built by Heimsoeth and Rinke in 1941, the oak-encased machine that encrypted German codes during the Second World War is the three-rotor version, used between 1938 and 1944.
The estimate for the sale at Bonhams in Knightsbridge is £40,000-£60,000.
Patented by HA Koch at the end of the First World War, this particular device was intended for commercial purposes but by 1939 the majority of Enigma machines had been appropriated for German military use.
The construction of the world's first top secret computing machine Colossus at Bletchley Park near Milton Keynes during the war helped in the cryptanalysis of the Lorenz cipher, an even more complex cipher machine than Enigma.
The Lorenz was used exclusively for the most important messages passed between the German Army Field marshals and their Central High Command in Berlin, and had to be cracked by carrying out complex statistical analyses on the intercepted messages.
Without the Collosus, the Allies would not have had vital intelligence about the German Army, which was credited with shortening the war.
Laurence Fisher, specialist head of mechanical music, technical apparatus and scientific instruments at Bonhams, said: "Enigma machines come up very rarely at auction.
"This particular example is in working order, completely untouched and un-restored.
"Many machines were picked up by the Allies as souvenirs during the final stages of the Second World War and as such, in later years, tended to be mixed and matched, where rotors, outer cases and head blocks were replaced with another machines' parts.
"This one has all elements bearing the same serial number, making this totally complete and original throughout."
Other notable pieces in the auction include a complete set of Enigma rotors, which are estimated to fetch up to £8,000.
The sale takes place on November 14.