Wrens working with an engineer on the replica Tunny machine
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WWII code-cracking computer rebuilt at Bletchley

A working replica of a computer that cracked secret Nazi messages in World War II has been completed.

Engineers at Bletchley Park in Buckinghamshire built the Tunny machine using discarded blueprints.

Up to 15 Tunny machines cracked the German Lorenz code at the height of the war, but the British government ordered their destruction when the conflict ended.

Engineer John Whetter and 1940s Tunny operator Helen Currie explain why they believe the mechanical computer reduced the length of the conflict.