(CNN) -- An encoding device synonymous with one of the most remarkable episodes of World War II espionage will go under the hammer in London later this month.

A version of the three rotor Enigma machine -- used by the German military to encrypt messages, the code of which was subsequently cracked by a team at the legendary Bletchley Park complex -- will be auctioned at Christie's on September 29.

Although the number of the ciphering machines still in existence is thought to remain in the thousands, "it is rare for one to come up for sale," says Christie's specialist, James Hyslop. "Many are believed to have been produced but it's not a particularly high survival," he adds.

During the wartime period, the Enigma machine was the most advanced device of its kind, a forerunner of the first modern computer systems.

Originally produced by a Dutch company for commercial use in the aftermath of the First World War, the technology was snapped up for sole use by the German military in 1929.

Employing a complex series of interchangeable rotors, the machine would encode messages before sending them via Morse code to an identical device in another location.

If the receiving Enigma was attuned to the same settings -- one of a possible 158 million million million combinations -- the encrypted message would then be automatically decoded.

The mindboggling numbers involved led the Germans to believe that it was "impossible to crack" the Enigma, Hyslop explains, hence its importance to the Nazi war machine.

Unbeknown to Hitler's charges however, a group of code breakers based at Bletchley Park in the English countryside had devised a way to do just that.

Led by the English mathematician Alan Turing, this small army of cryptologists, linguists, scientists and data analysts managed to create a system that at its peak was breaking as many as 6,000 encrypted German Enigma messages every day.

"The importance of the Enigma machine and the efforts of those at Bletchley to decode it cannot be underestimated," says Simon Greenish, Director of the Bletchley Park Museum.

"Historians have, until comparatively recently, recognized that Bletchley played a very significant part in the war, shortening it by at least two years," he says. "But some are now beginning to say that perhaps it made the difference in terms of winning (the war)."

The extraordinary efforts of those involved, Greenish adds, played a vital role in gathering the intelligence that helped shape pivotal battles such as D-Day, the Russian campaign, the North African campaign and the battle for the Atlantic.

Greenish claims the role played by the Enigma in determining the outcome of WWII alone is enough to guarantee its status as a relic of great historical importance.

But according to Hyslop, the machine's significance goes way beyond its wartime contribution.

Its technological complexity also makes it an attractive item to collectors of "early science, mathematics, history and computing instruments," he says.

"In November last year, we set the world record price (£67,250, $106,164) for an Enigma machine at auction," says Hyslop.

Given that the market for scientific devices of rich historical importance have remained unaffected by the financial downturn, he adds "we're hoping we might be able to push that again this time round."