Bletchley Park historians have recovered a rare machine used by Adolf Hitler to exchange top secret messages with his high command after finding it advertised on eBay for just £9.50 ($20.70).
Volunteers from the National Museum of Computing, based at the wartime code-breaking centre, tracked down the Lorenz teleprinter to a home in Southend, Essex, where it had been lying forgotten on the floor of a shed.
At first the researchers assumed they had snapped up a civilian version of the machine, but it was only when they discovered a swastika and unique military serial number they realised it was part of the system Hitler used to communicate with top field marshals such as Rommel.
While the famous Enigma system was used by the German war machine to exchange coded messages with frontline units, the more complicated and cumbersome Lorenz coding system was used to deliver detailed strategic messages exclusively to the eyes of the army commanders at static headquarters.
Cracking the code, which was achieved by Bletchley Park mathematician Bill Tutte, was one of the most significant British achievements of World War II, enabling General Dwight Eisenhower to establish that the allied decoy ahead of D Day had fooled the Germans, as well as helping the USSR win the crucial battle of Kursk.
Only 200 of the teleprinters, each of which accompanied a cipher coding machine, were ever manufactured and historians believe the vast majority were destroyed by German forces as they retreated at the end of the war.
John Wetter, a volunteer engineer at the National Museum of Computing, described the moment he realised the Lorenz teleprinter was part of Nazi high command apparatus.
"We saw the swastika and then we noticed one of the keys was devoted to the double lightning bolt symbol of the SS," he said.
"We'd simply never seen one before.
"It does make you wonder what kind of messages were sent and received on that particular machine, I must admit."
Unlike the Enigma system, which took a long time to send and receive messages, operators could enter lengthy messages in plain German into the Lorenz teleprinter relatively quickly.
They were then encrypted using the accompanying 12-wheeled cipher machine and transmitted on short-wave radio, where the process would be reversed by the recipient.
Once Tutte cracked the code, Bletchley's Colossus computer was used to translate the detail of individual messages sent by Lorenz in a matter of hours.
"We were able to drip-feed the Russians the locations of the German tank divisions of Kursk," said Wetter.
"The Russians never knew how we got the information, but it was the turning point in the war.
"It also gave Eisenhower the confidence to say 'go' on D Day, knowing the panzer divisions were all waiting in Calais and not Normandy."
The teleprinter was purchased by the museum in secret three years ago and they have been painstakingly refurbishing it since.
In recognition of the D-Day anniversary next month, it is being united with a Lorenz cipher unit, on loan from Norway's Armed Forces Museum, one of only four known to exist.
The National Museum of Computing has now appealed for help finding the system's only missing component, the electric motor.
"That will give us the chance to show the breaking of the Lorenz cipher code from start to finish," said Any Clark, museum chairman.
"We can show every single point in the process."