Heritage minister John Penrose has announced that Bletchley Park's Block C, in which the Enigma Code was cracked during World War II, has received Grade II listed status.
The building is now at the heart of plans to transform the site into a heritage centre, and was the location for the first high-speed data processing machines used to crack German codes.
Last month, it was
announced that Google had donated £550,000 towards the first phase of the £15m development - helping to match a £4.6m Heritage Lottery Fund grant.
Penrose said: "The work that took place at Bletchley Park was absolutely key to the Allied victory in World War II. Parts of the site already have listed status, and I'm pleased to add Block C to this group."