From 1978 to 1985, he held the position of director of the Department of Radiotherapy and Oncology, Royal Postgraduate Medical School, Hammersmith Hospital, London.
[3][4] He had been appointed to the temporary rank of captain by the time he was Mentioned in dispatches "in recognition of gallant and distinguished services in Burma" on 9 May 1946.
[5] After the Second World War, Halnan returned to Cambridge and gained admission to study medicine at UCL, London, from where he graduated.
[1][3][8] In 1967 he moved to Glasgow, where he later became involved in establishing the Beatson Cancer Centre and received the Fellowship of the Royal Society of Edinburgh.
[3] From 1978 to 1985, he held the position of director of the Department of Radiotherapy and Oncology, Royal Postgraduate Medical School, Hammersmith Hospital, London.