The collection includes some biographical material including Bretscher's own 'Survey of activities during the war and with the A.E.R.E', compiled in 1964 and a lecture given at Harwell in 1967 on 'Wartime nuclear physics and chemical research at the Cavendish Laboratory 1940-1944 associated with atomic weapons.' Very little remains of his early work in Switzerland and there is only a little material on the early stages of his atomic research at Cambridge and the collaboration with D. E. Lea. Much better documented is the work undertaken at the Cavendish Laboratory for the 'Tube Alloys' Project. There are research notes and reports by members of the team, reports prepared for the MAUD Committee and the Department of Scientific and Industrial Research, correspondence with J. Chadwick and others. The largest body of material relates to Bretscher's postwar work at the U.K. Atomic Energy Authority Research Establishment at Harwell with special reference to collaborative research projects and national and international nuclear data committees.