2023, book 3: Without Enigma: the Ultra and Fellgiebel riddles, Kenneth Macksey

The premise here is that the Axis became aware of the breaking of Enigma and phased it out in favour of Lorenz, code books, etc. It's OK. An interesting subject, but I would much prefer to read a regular history in parallel with the speculative one. The clarifying chapter endnotes that try to indicate where history and fiction differ are not clarifying enough, nor do I think the ordering works: the true history should come first. Anyway, it's OK. An interesting premise, but not executed terribly well.