Sigint and automation
Sigint and automation Even when remaining classified material is released, it will not be easy to assess the importance of Signals Intelligence to the Allied victory in World War 2. On the other hand, such has been the speed of development of machines that carry out tasks that were considered to involve thought, that—apart from the difficulties associated with secrecy—it is already possible to recognize that the cipher-breaking activities of the Government Codes and Cyphers School (GC&CS) at Bletchley Park, England played an important part in this development. The first of the large Bletchley machines was the “bombe,” an electromechanical device for finding the day‘s settings of the Enigma machines used to encrypt enemy radio messages. The name “bombe” is derived from that given to completely different apparatus employed by Polish cryptanalysts, led by Marian Rejewski, in their breaking of Enigma in the 1930s. The work at Bletchley remained entirely secret until the 1970s, and even after the site was opened to the public as a museum it was believed that the details of the bombes had been lost beyond recall. However, it turned out that GC&CS‘s successor, GCHQ, had blueprints, a dusty roll of papers held together with a perished rubber band. Working from these blueprints, a team led by John Harper is now well on the way to rebuilding a working bombe. The mechanical part was shown in operation at Bletchley Park on 10 September 2002, in the place where the originals were used, a grimly utilitarian building heavily fortified against bomb-blast (see Figure 1). The location was a reminder that we are not looking at “blue skies” research but at machines designed to carry out a single task precisely defined by wartime needs. Enigma machines had been in use for many years, and it was known how they worked. The method of breaking the cipher depended upon exploiting some of its known characteristics. The bombe was an array of Enigma emulators into which one put the message and a “crib,” that is a string of characters that one believed was contained in the plaintext of the message. The bombe then checked through possible initial settings of the rotors to find which settings were compatible with the crib. When it found one it stopped. As Alan Turing put it, “with the bombes you are not looking for an answer but looking to discard the answers that are no good to you.” The bombes were manufactured in Letchworth, by the British Tabulating Machine Company (BTM, later to become ICL). Its employees referred to themselves as “working down the Tabs,” and the site is now the Tabs Housing Estate. The only surviving buildings are the Spirella factory (used for sub assemblies) and the old Training Centre. Unlike the bombe building at Bletchley Park, the BTM works had no special protection; they were normal steel-framed structures. The Germans never hit them, but the Americans very nearly did: a fuel tank fell off a fighter returning from long-distance duty, and huge quantities of aviation fuel started a fierce fire less than a hundred yards away. A split second earlier and ... The bombe that Harper‘s group have rebuilt is one for attacking a 3-rotor Enigma machine. It is a substantial structure, the parts being assembled on a steel frame with base 2.21 m × 0.8 m, and height 1.78 m, mounted on heavy-duty castors. There are three sections, one above the other, each containing twelve columns of three wheels each. The three sections work independently, each on a separate set of solutions, but if one stops, on a possible solution, then all stop. The wheels and a multitude of connection rods are driven by a DC electric motor, originally connected to the mains through a mercury-arc rectifier. Such rectifiers are now banned for health and safety reasons (they pour out ultraviolet radiation), so the rebuild will have to compromise with authenticity in that respect. Otherwise, however, the machine has been made with great dedication to accuracy, engineering work being undertaken by local firms who set their apprentices to make parts as test pieces, and especially by members of the Society of Model Engineers. Before work began, some difficulties were smoothed out by the use of three-dimensional modeling, carried out by Warwick University Department of Computer Science. Much guidance was provided by Norman Hedges, who worked at BTM when the original bombes were being made there. The rebuilders have been impressed by how much effort must have gone into the original machines. Only 15 percent of the parts were standard items for BTM. It has become clear that the machines represented not only a considerable intellectual achievement on the part of the designers (Turing and Welchman of Bletchley Park and Events & Sightings