Why codebook captures can remain secret for generations

Why would Britain still avoid admitting codebook captures eighty years later?

Missing or closed files are one obstacle. Disclosure can also expose disputes with allies and prompt difficult questions about when intelligence arrived, whether commanders could act and whether action would reveal its source.

Missing records and complicated closure practices can make old intelligence operations difficult to reconstruct. Clarke describes several possible triggers for continued closure, including dates connected with participants, relatives and the handling of files. Dan proposes that disclosure might reveal coercion or manipulation used to obtain codebooks, but Clarke rejects the more elaborate spy-story explanation and emphasizes rapid recovery from ships and diligent work on the material. He instead stresses tensions over what Britain shared with allies and the consequences of revealing what commanders knew. Intelligence had to arrive and reach the right command in time to influence an operation. Acting on it could also reveal that a code had been compromised. Disclosure later raised painful questions about convoy losses, even though possessing intelligence did not guarantee that every ship could be saved.