The group was responsible for designing and debugging electronic circuitry. Although Williams was initially disappointed at being given someone with so little practical experience, Kilburn became a valued member of the team. On 14 August 1943, he married Irene Marsden, a shop assistant. They went on to raise a son, John, and a daughter, Anne. Kilburn's wartime work inspired his enthusiasm for some form of electronic computer. The principal technical barrier to such a development at that time was the lack of any practical means of storage for data and instructions. In July 1946, Kilburn and Williams collaboratively developed a storage device based on a cathode ray tube (CRT) called the Williams–Kilburn tube. A patent was filed in 1946. Initially they used it to store a single bit. The CRT image soon faded, so they devised a scheme by which it was read and refreshed continually, effectively making the data storage permanent. By December 1947, they were able to store 2,048 bits on one diameter CRT. In December 1946, Williams took up the Edward Stocks Massey Chair of Electrotechnics at the University of Manchester, and recruited Kilburn on secondment from Malvern. The two developed their storage technology and, in 1948, Kilburn put it to a practical test in constructing the Manchester Baby, which became the first stored-program computer to run a program, on 21 June 1948. He received the degree of PhD in 1948 for his work at Manchester, writing his thesis on "A storage system for use with binary digital computing machines" under Williams's supervision. Kilburn anticipated a return to Malvern but Williams persuaded him to stay to work on the university's collaborative project developing the Ferranti Mark 1, the world's first commercial computer. Max Newman withdrew from the project, believing that the development of computers required engineers and not mathematicians at this point, but Williams preferred to return to electrotechnics, leaving Kilburn in charge. He was assisted by Alan Turing, who arrived at Manchester in 1948. The Mark I incorporated innovations such as index registers, and combined CRTs with magnetic drum storage. Nine Mark I computers were sold by between 1951 and 1957. Over the next three decades, Kilburn led the development of a succession of innovative Manchester computers. The first, commenced in 1951, was a development of the Mark I known as the megacycle machine or Meg, that replaced the vacuum tube diodes with solid state ones. This permitted an order of magnitude increase in the clock rate.