Despite huge interest in the subject, encouraged by the film starring Steve McQueen, the tunnel remained undisturbed over the decades because it was behind the Iron Curtain and the Soviet authorities had no interest in its significance.
Many of the bed boards which had been joined together to stop it collapsing were still in position.
And the ventilation shaft, ingeniously crafted from used powdered milk containers known as Klim Tins, remained in working order.
Scattered throughout the tunnel, which is 30ft below ground, were bits of old metal buckets, hammers and crowbars which were used to hollow out the route.
A total of 600 prisoners worked on three tunnels at the same time. They were nicknamed Tom, Dick and Harry and were just 2 ft square for most of their length.
It was on the night of March 24 and 25, 1944, that 76 Allied airmen escaped through Harry.
Barely a third of the 200 prisoners - many in fake German uniforms and civilian outfits and carrying false identity papers - who were meant to slip away managed to leave before the alarm was raised when escapee number 77 was spotted.
Only three made it back to Britain. Another 50 were executed by firing squad on the orders of Adolf Hitler, who was furious after learning of the breach of security.
In all, 90 boards from bunk beds, 62 tables, 34 chairs and 76 benches, as well as thousands of items including knives, spoons, forks, towels and blankets, were squirrelled away by the Allied prisoners to aid the escape plan under the noses of their captors.
Although the Hollywood movie suggested otherwise, NO Americans were involved in the operation.
Most were British, and the others were from Canada , (all the tunnellers were Canadian personnel with backgrounds in mining) Poland, New Zealand, Australia and South Africa.
The latest dig, over three weeks in August, located the entrance to Harry, which was originally concealed under a stove in Hut 104.
The team also found another tunnel, called George, whose exact position had not been charted. It was never used as the 2,000 prisoners were forced to march to other camps as the Red Army approached in January 1945.
Watching the excavation was Gordie King, 91, an RAF radio operator, who was 140th in line to use Harry and therefore missed out.