Pages 262-3: Alexander's period in charge of Naval Enigma is fully described in his Cryptographic History of Work on the German Naval Enigma (see the Update notes on chapter 4). In particular he notes that Joan Clarke remained in the Naval Enigma section until the end of the war. In June 1943:
Joan Clarke, who had formerly been one of the best Banburists in the section, now joined Mahon, Pendered and Noskwith and these four coped with the whole of the cryptographic work for the rest of the war. This was a very fine achievement and meant extremely hard work for all four: 6 major keys (Dolphin, Shark, Porpoise, Plaice, Bonito and - from September 1944 - Narwhal) were regularly broken, the associated Offizier keys were usually read when they carried any appreciable volume of traffic and a number of lesser keys were broken intermittently.
Page 266: 'The Turing theory of statistics' was indeed vital in the breaking of the Lorenz cipher systems, the so-called 'Fish' work. This is often neglected, attention being focused on the outstanding innovation in electronic engineering. But without the statistical brilliance, there would have been no operations for the new machinery to carry out. The release of the substantial General Report on Tunny makes the debt to Turing's theory clear. Its pages are full of the application of Bayesian statistics, weight of evidence, deciban counting, and advanced calculations in probability theory. The direct connection with AMT and the earlier work of Hut 8, from which Jack Good brought with him when transferred to the Fish work, is made clear.
A transcription of the General Report on Tunny is made available on Graham Ellsbury's website.
Page 270: In contrast to Bletchley Park, Hanslope Park has remained a secret British Government facility, with a very low profile. See this Guardian news report from 2013.
Page 277: There is an on-line description of the machines and an account of the partial rebuilding of one by the late Tony Sale on his site.
There were actually ten Colossus machines. The following summary is given in the General Report on Tunny, page 35:
. . . Colossus I was delivered in February, 1944, and immediately sent up the output to more than twice its previous level. Colossus was entirely the idea of Mr. Flowers of Dollis Hill. . . A preliminary order for four further Colossi was placed in March, 1944, increased to twelve at the end of April . . . Great pressure was put on Dollis Hill to deliver the Colossi quickly and they promised on the 14th March to have Colossus 2 (i.e. the first production model) working by 1st June. This promise they fulfilled. Colossus 2 came into action on 1st June at 0800. The remaining Colossi followed at the rate of about 1 a month. A new building (Block H) was erected to house Colossi 5 to 11. Its plans were approved on 25th May, 1944 and it was ready for occupation on 17th September. Work on assembly of Colossus 11 had started on 8th May, 1945 and was stopped (before completion) a few days later.Page 278: The day of the invasion of Normandy, 6 June 1944, was actually the exact date of AMT's progress report on the Delilah, released from secrecy in 2004. See the document on this Turing Sources page.
Page 299: Thomas Goldstrasz and Henrik Pantle kindly brought to my attention the assertion in my original text that Zuse's calculators were used on the construction of V2 rockets. This was incorrect. Zuse machines were in fact used on aircraft design, but the significant point is how little the German war effort harnessed his ideas. This blunder was corrected in the Walker Books 2000 edition, and in all 2012 and later editions.
Page 304 and note 5.26: Conventional history of the origin of the computer still emphasises a primary role for von Neumann. Yet in describing Turing's origination of the computer as something done with 'marked independence' of von Neumann, I may well have understated both Turing's originality and his actual influence. It can be argued that Von Neumann was greatly assisted by knowing Turing's formulation of computability. The logician Martin Davis's book The Universal Computer, The Road from Leibniz to Turing (2000) makes this claim very clearly.