Douglas Rayner Hartree FRS (27 March 1897 – 12 February 1958) was an English mathematician and physicist most famous for the development of numerical analysis and its application to the Hartree–Fock equations of atomic physics and the construction of a differential analyser using Meccano.

[7] According to Hill, writing in Hartree's obituary, ‘Quietly one day he improvised a long-base height-finder out of some wires, posts, and a steel tape’.

After the end of World War I, Hartree returned to Cambridge graduating in 1922 with a Second Class degree in natural sciences.

Today, the Hartree-Fock equations are of great importance to the field of computational chemistry, and are applied and solved numerically within most of the density functional theory programs used for electronic structure calculations of molecules and condensed phase systems.

In time, the group consisted of four members[12] (Jack Howlett, Nicholas R. Eyres, J. G. L. Michel, Douglas Hartree, and Phyllis Lockett Nicolson).

Problems were submitted to the group without information about the source but included the automatic tracking of targets, radio propagation, underwater explosions, heat flow in steel, and the diffusion equation later found to be for isotope separation.

A differential analyser could have been used if more integrators had been available, so Hartree set up his group as three "CPUs" to work on mechanical desk calculators in parallel.

[13] Hartree never published any of his magnetron research findings in journals though he wrote numerous highly technical secret reports during the war.

In April 1944 a committee which included Hartree recommended that a mathematical section be set up within the National Physical Laboratory (NPL).

Hartree recommended the grant but Darwin opposed it on the grounds that Turing's ACE at NPL would be sufficient to serve the needs of the country.

Hartree did further work in control systems and was involved in the early application of digital computers, advising the US military on the use of ENIAC for calculating ballistics tables.

In the summer of 1946 Hartree made his second trip to ENIAC as an evaluation of its applicability to a broad range of science, when he became the first civilian to program it.

In October he gave an inaugural lecture entitled "Calculating Machines: Recent and Prospective Developments and their impact on Mathematical Physics".

He said: "..there are, I understand many problems of economic, medical and sociological interest and importance awaiting study which at present cannot be undertaken because of the formidable load of computing involved."

On 7 November 1946 The Daily Telegraph, having interviewed Hartree, quoted him as saying: "The implications of the machine are so vast that we cannot conceive how they will affect our civilisation.

"[15] Hartree's fourth and final major contribution to British computing started in early 1947 when the catering firm of J. Lyons & Co. in London heard of the ENIAC and sent a small team in the summer of that year to study what was happening in the US, because they felt that these new computers might be of assistance in the huge amount of administrative and accounting work which the firm had to do.

The team met with Col. Herman Goldstine at the Institute for Advanced Study in Princeton who wrote to Hartree telling him of their search.

[16] Hartree's last PhD student at Cambridge, Charlotte Froese Fischer, became known for the development and implementation of the multi-configuration Hartree–Fock (MCHF) approach to atomic structure calculations and for her theoretical prediction concerning the existence of the negative calcium ion.