Born in Treorchy in the Rhodda Valley on 7 July 1924. In July 1925 his father died and Davies moved with his mother and twin sister to Portsmouth to live with his maternal grandmother and aunt. In 1941, on the completion of his school education at the Portsmouth Boys Southern Secondary School, he took up a 'Royal' Scholarship at Imperial College London where he studied physics. In 1943 he graduated with first-class honours and was directed to work at Birmingham University as a research assistant in the Tube Alloys Project (the British contribution to the development of nuclear weapons) under R.E. Peierls and later A.H. Wilson. Davies's main work was concerned with the stability and control problems for the gaseous diffusion plant. In 1944 he continued to work for the Tube Alloys Project at ICI, Billingham, on Teeside and in 1945 at the close of the project he returned to Birmingham to work in the Physics Department under M.L.E. Oliphant. The overlap between the courses at Imperial College allowed Davies to complete the requirements for a mathematics degree in a year and he resumed the scholarship for that purpose, graduating with first class honours in 1947.
The National Physics Laboratory was setting up a group to build a stored program computer under the direction of A.M. Turing and Davies joined this group and began working on the logic design and later the building of the ACE Computer. When the Pilot ACE was built, Davies became a user, working on a variety of simulations, including the behaviour of road junctions controlled by traffic lights. In 1954 Davies was awarded a Harkness Fellowship to study in the USA. He came to view his choice of MIT as an error because all the interesting computer work was classified. The period at MIT was interrupted by a special mission for the United Nations, investigating a request from the Indian Statistical Institute, Calcutta for funds to buy equipment from the USSR. Subsequently he was involved for a number of years on two new projects. One was the development of the cryotron, a superconducting device with potential for the large-scale integration of logic and storage. However, efforts in this area foundered on engineering problems of many kinds. The other was the translation by computer from Russia to English. Davies concluded that although 'we were not able to set up a serviced based on this work 'it is noteworthy that our real experience' was very different from the accepted public view of machine translation.
In the early 1960s time-sharing whereby a large computer gave an online service to a number of users was very much the coming thing. In 1965 Davies proposed, in a privately circulated paper, the principle for a data communication network which he subsequently named 'packet switching'. In March of the following year he lectured to a large audience, advocating the use of techniques in a public switched data network. In 1966 Davies was appointed Superintendent of the Division of Computer Science where the programme of research included data communication systems, information systems, pattern recognition and man-computer interaction. The data communication proposals for specialised networks using packet switching were widely publicised in 1967 and greatly influenced the early development of ARPA Network. Davies successfully promoted packet switching for public networks at the CCITT (International Consultative Committee for Telephones and Telegraphs) and elsewhere. In 1973 he published (with D.L.A. Barber) Communication Networks for Computers and in 1979 (with Barber, W.L. Price and C.M. Solomonides) Computer Networks and their Protocols. In 1975 Davies received the John Player Award of the British Computer Society for his work in packet switching and shared the IEEE (Institute of Electrical and Electronics Engineers) Internet Award for 2000 for work on packet switching.
In 1978 Davies was given the status of an 'individual merit' appointment at the NPL enabling him to relinquish administrative responsibilities, and he led a small research team concerned with security of data in networks. The team developed the application of cryptographic methods to the practical work of network security, especially the use of asymmetric (public key) cryptography. Consulting work under contract to financial institutions and others provided the practical experience. After Davies retired from NPL in 1984, he provided consultancy to financial institutions on high value payment systems and advised suppliers and users of secure systems of many kinds, for example mobile telephony and direct broadcast satellite television. In 1984 he published (with W.L. Price) Security for computer networks: an introduction to data security in teleprocessing and electronic funds transfer. Davies also pursued his interest in cryptography as a hobby with research on Second World War cipher machines and published an number of articles on the topic.
Davies was appointed CBE in 1983 and elected to the Fellowship of the Royal Society in 1987. In 1955 Davies married Diane Burton which whom he had three children. He died on 28 May 2000
From the guide to the DAVIES, Donald Watts (1924 - 2000), 1936 - 2004, (Imperial College London)