During the Second World War, Curran worked with others in the UK on the development of centimetre radar and then in the USA on the Manhattan Project (the development of the atomic bomb) where he worked on the research and design of isotope electromagnetic separators.
He used his American knowledge of the synchrotron concept to assist Philip Dee and Walter MacFarlane in the installation of a 300 Mev Synchrotron at Glasgow. During this period, he invented the modern gas-filled proportional counter for the detection and counting of radiation sources. This device is used in almost every scientific laboratory in the world.
The 21 August 1948 edition of Nature contains a terse description of the new technique as the second paragraph in a letter on the beta decay of tritium.
He subsequently worked at Harwell and then became chief scientist of the Atomic Weapons Research Establishment at Aldermaston for a year before returning to Glasgow as Principal of the Royal College of Science and Technology.