text: During the Second World War Hartree supervised two computing groups. The first group, for the Ministry of Supply, has been described by Jack Howlett as a "job shop" for the solution of differential equations. At the outbreak of World War II, the differential analyser at the University
  of Manchester was the only full-size (eight integrator)
  differential analyser in the country. Arrangements were made to have the machine available
  for work in support of the national war effort. In time, the group consisted of four members (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. The second group was the magnetron research group of
  Phyllis Lockett Nicolson, David Copely, and Oscar Buneman.
  The work was done for the Committee for the Co-ordination of the Valve Development assisting the development of radar. 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. For a method of solution, he selected what is now a classical particle simulation.
  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). In October this recommendation was put into effect with its first two objectives being the investigation of the possible adaptation of automatic telephone equipment to scientific equipment and the development of electronic computing devices suitable for rapid computing. One suspects that some members already knew of the Colossus computer. John R. Womersley (Turings bête noire) was the first Director. In February 1945 he went on a two-month tour of computing installations in the US, including visiting ENIAC (still not complete). He became acquainted with drafts of von Neumanns famous June 1945 EDVAC report. About two months later Hartree also went over to see ENIAC, not then publicly known.