LONDON.- Examples of key machines in the history of 20th century cryptology from Germany, Sweden, Switzerland and Russia are on offer at Bonhams Scientific, Technological and Mechanical Music Instruments in London on Tuesday 27 October.

Led by a very rare four-rotor M4 Enigma machine from 1941 (lot 52 £80,000-120,000), the sale also includes:

• A Swedish Hagelin B-21 cipher machine from 1932 (lot 48 £40,000-60,000);

• NEMA enciphering machine (lot 47 £10,000-15,000) built in Switzerland and originally developed during World War II when the Swiss discovered that German and Allied forces were intercepting their military traffic;

• Falka M-125 three-rotor cipher machine (lot 49 £7,000-10,000) used extensively by Soviet Russia and Warsaw Pact countries during the Cold War.

Bonhams’ technology specialist Jon Baddeley said, “It’s unusual to find so many different types of cipher machines in one sale. The German Enigma is, of course, well known, but the others are fascinating variations on a theme and reflect the central role of protecting intelligence before, during and after World War II.”

The Germans developed the four-rotor Enigma machine for use by its navy and in particular to make communications secure during the Battle of the Atlantic. The cryptology team at Bletchley Park had cracked the three-rotor enigma – the story is told dramatically in the 2014 film The Imitation Game – but faced a much tougher assignment in tackling the four-rotor version because the number of possible key was increased by a factor of 26.

The simplest way of cracking the naval enigma was to capture the German code books. The creator of James Bond, Ian Fleming, then working in naval intelligence, suggested crashing a captured German bomber in the English Channel near a German ship. When the ship sailed to the rescue, the British soldiers hidden on the bomber would overcome the crew and steal the codes. In the end, more conventional raids on U-boats and weather ships secured the precious books.

The machine in the sale, which was made for use by the Navy High Command in Norway, is extremely rare. Not only were the naval M4 Enigmas made in much smaller quantities than the three-rotor army machines, most of them were lost either in action or when the German Navy scuttled its ships at the end of the war.