Turing and the origins of digital computers
In this chapter I describe my initial attempts at investigating, during the early 1970s, what Alan Turing did during the Second World War. My investigations grew out of a study of the work of Charles Babbage’s earliest successors—in particular, the Irish pioneer Percy Ludgate—a study that led me to plan an overall historical account of the origins of the digital computer. The investigation resulted in my learning about a highly secret programmable electronic computer developed in Britain during the Second World War. I revealed that this computer was named Colossus, and had been built in 1943 for Bletchley Park, the UK government’s wartime codebreaking establishment. However, my attempt to get the details of the machine declassified were unsuccessful, and I came to the conclusion that it might be a long time before anything more would become public about Bletchley Park and Colossus. Around 1970, while I was seeking information about the work of Charles Babbage and Ada Lovelace to use in my inaugural lecture at Newcastle University, I stumbled across the work of Percy Ludgate. In a paper he wrote about Babbage’s ‘automatic calculating engines’, Ludgate mentioned that he had also worked on the design of an Analytical Engine, indicating that he had described this in an earlier paper in the Proceedings of the Royal Dublin Society.From a copy of that paper I learned that an apparently completely forgotten Irish inventor had taken up and developed Babbage’s ideas for what would now be called a program-controlled mechanical computer. Previously I had subscribed to the general belief that over a century had passed before anyone had followed up Babbage’s pioneering 1837 work on Analytical Engines. This discovery led me to undertake an intensive investigation of Ludgate, the results of which I published in the Computer Journal. With the help of a number of Irish librarians and archivists I managed to find out quite a few details about the tragically short life of this Irish accountant, and even to make contact with one of his relatives. Unfortunately, I found nothing more about his design for a paper-tapecontrolled analytical machine beyond what was given in his 1909 paper. My investigations into the background to Ludgate’s work left me with a considerable amount of information on pre-computer technology and on other little-known successors to Babbage.