Just before
World War II began, Gunn worked for three months with the thermodynamicist
R.H. Fowler. He worked in the Admiralty scientific service from 1940 to 1945. He was part of a team of scientists and engineers led by
Harrie Massey based first at
Teddington, and then at the
Admiralty Mining Establishment attached to
HMS Vernon at
Portsmouth. He was involved in researching countermeasures against
German magnetic mines and in the development of a range of British non-contact mines. The team included many young physicists who would go on to make major scientific contributions, among them
Francis Crick. In 1943, while still working at the Admiralty, Gunn was elected to a research fellowship at
St John's College, Cambridge, but after the war he chose instead to accept a lectureship in applied mathematics at
Manchester University. There he worked with Professor
Sydney Goldstein, a mathematician noted for his contribution to
fluid dynamics, and wrote papers on supersonic flow and turbulence. In 1946, Gunn became a lecturer in Professor Harrie Massey's department in
University College London, where he carried out research in nuclear and
particle physics. During his three years at
University College London, his focus shifted from classical applied mathematics to the quantum mechanical subjects of nuclear physics and particle physics. Gunn then went to work at
Glasgow University, where the Natural Philosophy Department, under its new chairman, Philip Dee, was branching out into nuclear physics. Dee wished to turn Glasgow University into a leading centre of expertise in nuclear and particle physics. This development provided Gunn with an opportunity to explore his newfound interest in those subjects. He was appointed to the
Cargill Chair in Applied Physics in 1949. The chair had been founded in 1920 and endowed by Sir John Traill Cargill of the Burmah Oil Co. Gunn would hold the chair until 1982. During his time at Glasgow University, Gunn collaborated with
Edwin Power, who had been his student at University College, and
Bruno Touschek, a physicist from Germany, to produce
mesons in proton collisions. This work helped marked the establishment of the field of particle physics. With Professor
Philip Dee, Gunn received funding for nuclear physics research, which allowed him and his colleagues to build a linear electron accelerator. After Touschek moved to
Rome, Italy, in 1953, Gunn collaborated with John Irving on the photodisintegration of light nuclei, which later became known as "Gunn-Irving wave functions". Later, Gunn played a notable part in the development of the
electron accelerator at Daresbury in northern England, and helped arrange for the construction of a linear electron accelerator near Glasgow. Radiation from accelerating electrons at Daresbury proved to have a multitude of practical applications. He also actively supported the Glasgow Project, which sought to detect cosmic gravity waves. This project has been described as giving "much of the early impetus to international work in this field.” He also was active in recruiting members of "three distinct theoretical research groups" at Glasgow University, "one of which remained active into the twenty-first century." Gunn retired from his position as professor of natural philosophy and Cargill chairman in 1982. In 1968, Gunn became a member of the
Science Research Council, and was its chairman from 1970 to 1972. It was during his period as chairman that the British government agreed to take part in the CERN project in Geneva, which proved critical to the development of European particle physics. He became a member of Glasgow University's grants committee in 1973 and was chairman of its Equipment Sub-committee until 1976. From 1976 to 1981, he was chairman of the university's physical sciences sub-committee. He was vice-principal of Glasgow University from 1972 till 1977 and dean of faculties from 1988 to 1992. ==Death==