The Colossus series of electronic computers, considered by some to be the first fully electronic (as opposed to electromechanical) computer in the world, was originally a British state secret. This means that many documents pertaining to the computers, including original blueprints, were destroyed.
However, enough information remained for the Computer Conservation Society to later build a working almost-replica of a Colossus Mark II. A search of their website and cursory examination of the National Museum of Computing (where the Colossus rebuild is housed) showed no signs of any schematics for the Colossus Mark II, its reconstruction or in fact any Colossus at all. Where can these schematics be found?