Alan Turing: The Enigma (77 page)

In 1946 people still believed that the great war surplus of scientific and technical advance could be turned to good use, although Mountbatten’s comments on ‘responsibilities’ reflected the fact that few had any idea of how this was going to be achieved.

The ENIAC had been released from military secrecy months before, and Hartree had written about it in the scientific journal
Nature
,
²¹
but it needed Mountbatten to make it ‘news’. He had taken his information from the NPL, and the inaccurate reference to chess-playing machines would suggest that he heard an excited Alan Turing talking about the future possibilities of the ACE. (There was, of course, no machine in existence that could play chess.) Darwin and Hartree were embarrassed not only by Mountbatten getting the wrong ends of the technical sticks, but also by his perfectly correct assertion that the ACE would exercise ‘hitherto human
prerogatives of choice and judgment’. They did not like to criticise Mountbatten, but wrote
²²
to
The Times
complaining that its headline ELECTRONIC BRAIN had given a false impression.
^*

The official NPL press release,
²³
on 6 November, was very different in tone. It presented the building of the ACE as a somewhat distant possibility, rather than being just round the corner. Correctly it set the origin of the ACE in Alan’s ‘severely mathematical paper’ of 1936, and explained how electronic switching provided the speed to make such a machine practical. It explained the superiority of the ACE over the ENIAC, through its large memory store, and referred to the work already done on programming instruction tables. But the cost had now risen to a figure ‘in the region of £100,000 to £125,000’ and it was stated that ‘It will be two or three years before the completion of this machine can be hoped for, since its construction presents formidable problems, both mathematical and technical.’

Now that this stirring if remote prospect had at last been entrusted to the British public, the
Daily Telegraph
showed itself the most eager to spread the good tidings, which it imbued with a suitably patriotic flavour. The headline BRITAIN TO MAKE A RADIO BRAIN/‘Ace’ Superior to US Model/ BIGGER MEMORY STORE appeared on 7 November, followed up next day with an account by its own reporter, who had interviewed Hartree, Womersley, and Alan at the NPL:

‘ACE’ WILL SPEED JET FLYING

…Revolutionary developments in aerodynamics, which will enable jet-planes to fly at speeds vastly in excess of that of sound, are expected to follow the British invention of ‘Ace’, which has been commonly labelled the electronic ‘brain’.

…Professor Hartree said: ‘The implications of the machine are so vast that we cannot conceive how they will affect our civilisation. Here you have something which is making one field of human activity 1,000 times faster.

In the field of transport, the equivalent of Ace would be the ability to travel from London to Cambridge …in five seconds as a regular thing. It is almost unimaginable.

…Dr Turing, who conceived the idea of Ace, said that he foresaw the time, possibly in 30 years, when it would be as easy to ask the machine a question as to ask a man.

Dr Hartree, however, thought that the machine would always require a great deal of thought on the part of the operator. He deprecated, he said, any notion that Ace could ever be a complete substitute for the human brain, adding:

’The fashion which has sprung up in the last 20 years to decry human reason is a path which leads straight to Nazism.’

The Germans, like the computer, had only been obeying orders, but this allusion did not deter Alan when next day a reporter from the local
newpaper came to investigate the ‘New NPL Wonder’. He only lengthened the time-span of his prophecy. They published the interview
²⁴
of the ‘34-year-old mathematics expert’ under the headline ELECTRIC BRAIN TO BE MADE AT TEDDINGTON:

Dr Turing, speaking about the ‘memory’ of the new brain …said it would be able to retain for a week or more about as much as an actor has to learn in an average play. Asked about Lord Louis Mountbatten s statement that it would be able to play an average game of chess, Dr Turing said that was looking far into the future. …The point was then put to him that chess and similar activities required judgment as well as memory, and Dr Turing agreed that that was a matter for the philosopher rather than the scientist. ‘But,’ he added, ‘that is a question we may be able to settle experimentally in about 100 years time.’

This was the most exciting if embarrassing thing to happen at the NPL for a long while, and Darwin was sufficiently encouraged to make a radio broadcast
²⁵
, in which he outlined the ‘idealised machine’ of
Computable Numbers
, and explained that ‘Turing, who is now on our staff, is showing us how to make his idea come true.’ But as the newsreel music faded away, the awkward fact remained that it was now nearly a year since Alan had shown in detail how to ‘make his idea come true’, and Darwin still did not know how the NPL was to give effect to his proposals.

On 22 October, when Hartree enquired about progress on the ACE, Darwin had to confess that ‘Post Office assistance had not been as great as was expected.’ On the TRE side, there had been more technical progress, since F.C. Williams had begun in about June to investigate the behaviour of spots on cathode ray tubes with a view to creating a storage system. During the war he had seen attempts at the Massachusetts Institute of Technology radar research laboratory to employ ordinary cathode ray tubes for echo cancellation, attempts which failed because of the transience of the spots, which faded in a second or so. But during the autumn of 1946, he had the idea, independently of Alan’s proposal in the ACE report, of refreshing the spots periodically to overcome this problem.
²⁶
He had also seen a way to do it. On the other hand, from an administrative point of view there had been a setback to NPL’s plans, since Williams had accepted the chair of electrical engineering at Manchester University – an appointment which he believed he owed to Blackett. Darwin explained to the Executive Committee that

He had also hoped that considerable assistance could be obtained from Dr F.C. Williams of TRE, but that he now understood that Dr Williams had accepted a University appointment. He said that he would explore the possibility of Dr Williams working on this project at his University – perhaps with the help of NPL or TRE staff …

The possibility, thin as it was, was indeed duly explored. On 22 November 1946, Williams, together with two other top TRE men R. A. Smith and A. Uttley, made a visit to the NPL ‘to discuss with Mr Womersley and Dr
Turing in what way help could be given to the ACE project.’ The official minutes
²⁷
were a masterpiece of discretion, Darwin being furious that Williams had been seduced into the Manchester orbit. Speaking alone with Smith, he banged on the negotiating table:

The Director emphasised the extreme importance which he attached to the development of ace, and put it as having the highest priority in his opinion of any work that was being done for DSIR at TRE. He was most anxious that some effort should be set aside for work done on this project.

Smith explained that this was very difficult. ‘Apart from the small number of staff now working for Dr F.C. Williams most of the able circuit technicians had been transferred to the Department of Atomic Energy’ – a statement reflecting another post-war story. So ‘the only way in which TRE could continue to contribute would be to second a small number of staff …to work under Dr Williams’ direction at Manchester University.’ This was not at all what Sir Charles Darwin wanted to hear, but he did not give up. The meeting was enlarged to include Williams and Uttley from TRE, and Womersley for the ν PL, while Alan was allowed in as well. In the discussion of the ACE

…It appeared that although an elaborate paper design had been laid down, the fundamental problem of storage of information had not been solved and that, as had been suspected, the experimental work of Dr Williams’ at TRE on storing information on a cathode ray tube was considerably in advance of the work which the Post Office were doing on the use of delay lines for storage purposes. …

Williams had, in fact, already succeeded in storing a spot on a cathode ray tube for an indefinite period. A compromise formula was agreed, according to which Williams’ work ‘should continue with as little disruption as possible’. The NPL drafted a contract for Williams to sign, according to which he would develop both electronic storage and components for the arithmetical hardware.

There was, however, a triple misunderstanding. For one thing, there was still the strong possibility of Manchester funding allowing Williams to develop his storage independently of NPL requirements. For another, the ACE design and programming had been done for a delay line store, and would have to be completely reworked if policy changed to the use of cathode ray tubes. Very probably Darwin and Womersley did not appreciate that the storage medium effectively dictated many aspects of the design of the machine and its programming. Alan might not have minded rewriting everything if it meant that progress could be achieved, but there was a deeper difficulty. While Darwin spoke as though he had had a ‘mathematician’ to lay down a design, and now was finding a practical man to build it, Williams’ attitude was that he was negotiating for funds wherewith to construct
his
computer. They were talking at cross-purposes. Success would depend upon bridging that gap, so closely tied in with social class, between ‘mathematics’ and ‘engineering’. But the crossing of demarcation lines was very difficult now. No longer was Germany enforcing cooperation upon its enemy.

Hartree, wanting to see more cooperation, took the next step. On 19 November he explained to Darwin that ‘Mr Wilkes was prepared to give as much help as he could on the ACE as he had facilities at Cambridge; he had experience of making up [delay] lines and would exchange information with Dr Turing.’ Next day Wilkes wrote
²⁸
to Womersley:

I believe Professor Hartree
has told you that I am beginning to do a little work on electronic calculating machines and that I am anxious to co-operate with you. As you know I recently paid a visit to the United States and saw what they are doing over there. Professor Hartree said he had discussed the matter with you and thought perhaps we might be able to make some mutually advantageous arrangement.

Wilkes visited the NPL a week later, on 27 November, to discuss his plans. On 2 December he wrote again:

I have been thinking over in more detail the subject we were discussing last Wednesday and what I have now in mind is that I should build up a group here containing about eight people of varying grades in addition to the mechanic and boy who are at present in the workshop. This would involve an annual wage bill of something like £2,500. In addition there will be cost of materials and getting things made outside.

I am quite convinced that the construction of a pilot model of some sort is an essential step in designing ACE.
^*
I do not see how else one can test out such things as control circuits. I am attaching a note I have written on the design of the pilot model and I think it would be a good thing if you decide to place a contract with us to call for this specifically. It does not follow that no part of ace may be ordered until the pilot model is finished but there will be many matters which it will be hard to settle, without experience at least of trying to get a pilot model working.

But the attached note outlined the specification of a computer on the EDVAC model, and thus entirely different from the ACE. Not only did it employ a central accumulator, but it ran counter to the Turing philosophy of keeping the hardware as simple as possible, and putting the work into the programming. Instead, it made the programming as easy as possible, at the cost of requiring electronic circuits to do the work of recognising and executing the various arithmetical instructions. Wilkes wrote apparently in ignorance of the fact that at the NPL they already had Version VII of a detailed design, for which six months’ hard work had been put into writing programs. Even to contemplate Wilkes’ proposal, as Womersley apparently
did, was to undermine his own division’s work. On 10 December he passed the proposal to Alan, whose reaction was understandably brusque:

Mr Womersley:

I have read Wilkes’ proposals for a pilot machine, and agree with him as regards the desirability of some such machine somewhere. I also agree with him as regards the suitability of the number of delay lines he suggests. The ‘code’ which he suggests is however very contrary to the line of development here, and much more in the American tradition of solving one’s difficulties by means of much equipment rather than by thought. I should imagine that to put his code (which is advertised as ‘reduced to the simplest possible form’ ) into effect would require a very much more complex control circuit than is proposed in our full-size machine. Furthermore certain operations which we regard as more fundamental than addition and multiplication have been omitted.

It might be argued that if one is to have so little memory then it is necessary to have a complex control to make up. In so far as this is true I would say that it is an argument for either having no pilot model, or for not using it for serious problems. It is clearly rank folly to develop a complex control merely for the sake of the pilot model. I favour a model with a control of negligible size which can later be expanded if desired. Only test problems would be worked on the minimal machine.