The Lorenz cipher had been broken and the structure of the machine that created it had been brilliantly worked out. Messages were being deciphered but sometime late in 1942 it was realised that the increasing volume of traffic was overwhelming.
Max Newman, who headed up the Newmanry which aimed to develop machines to accelerate the codebreaking, requested that a machine be made that would compare a paper tape that held the enciphered message with another tape that contained the key.
The German operators often -- and counter to instructions -- used the same wheel settings for more than one message. So once these settings had been discovered, that same key would decode later messages sent with the same wheel settings. This was to change when the Germans changed the settings more frequently, but this came later.
Although the cryptographers had the key, they didn't know the start positions of the twelve wheels and Newman had showed that the process of finding these start positions could be done by a machine within a reasonably short time. To do the same thing by hand would take just too long - this was the height of World War II and pressure from the powers above must have been immense.
Thus Robinson came in being. It was a joint effort between the Post Office and the Telecommunications Research Establishment at Malvern. Robinson was initially a machine that would make logical decisions between two paper tapes, each one at least 2000 characters long. It would compare one tape with the other and count the number of times certain conditions existed. One tape was one character shorter than the other, so the next time the two tapes ran through (each was in a continuous loop), they would be in different relative positions. The designers were aiming for a tape speed of 2000 characters per second, a hope that proved difficult to achieve.