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In final part of his walk-through, John Whetter from Bletchley Park, explains the use of Tunney in deciphering the German Lorenz code.

John Whetter, one of the Bletchley Park volunteers, continues his walk-through of how we cracked Lorenz, this time with the help of Colossus, the world's first programmable electric computer.

At Bletchley Park we talk to John Whetter, one of the Park volunteers, who walks us through the process to break and read Lorenz, the most complex code the Germans had.

We're at Bletchley Park again, talking to the code breakers, this time Baroness Trumpington talks about how she got involved in the service and the work she did at the Park.