In 1953, St Johnston left the British Non-Ferrous Metals Research Association and joined Borehamwood Laboratories of Elliott Brothers Ltd, where she worked in the Theory Division. The company was an early computer company and had produced its first computer in 1950. St Johnston learned to programme at the company and also at the 1954 Cambridge Summer School on Programming and, showing a real flair for programming, began working on EDSAC and the Elliott 400 and 800 series computers. By 1954, St Johnston was responsible for the programming of the Elliott 153 Direction Findingdigital computer for the Admiralty and soon after for programming Elliott’s own payroll computer; her work was said to have been inventive and structured, but also very accurate, hardly ever requiring ‘de-bugging’.
Vaughan Computers
Shortly after her marriage to Andrew St Johnston - head of the Elliott computing department - in 1958, St Johnston founded Vaughan Programming Services in Hertfordshire in 1959, taking software contracts, and training and hiring additional programmers as needed. On its tenth anniversary in 1969, company literature stated that "VPS was the first registered independent Software unit in the UK, that was not a part of a computer manufacturer, not a part of a computer bureau, not a part of a users' organisation and not a part of a consultancy operation." Very significant contracts came to St Johnston and VPS, such as programming early nuclear power stations, but in 1970 she branched out into hardware, producing her own computer, the 4M, and the company changed its name to Vaughan Systems and Programming in 1975 to reflect the new area of work. One of the 4M Vaughan computers is in The National Museum of Computing. St Johnston and Vaughan produced software for companies like the BBC, Unilever, and GEC, flight simulators for the RAF and software that provided real-time information for passengers on British Rail, the type of work for which the company became most well known. The company became well known for transport signalling and display systems.
Later life
In 1996, Vaughan Systems and Programming was sold to Harmon International, an American railway signalling company. St Johnston continued programming until the mid-1990s. She retired in 1999 and died on 30 June/1 July 2007.
