Relationship with the United States. In the late 1950s there was domestic and international pressure to discontinue atmospheric nuclear testing. Penney headed the UK delegation at a conference convened in Geneva on 1 July 1958. Macmillan took Penney along as an advisor to the conference in Bermuda in December 1961, where Macmillan met with President John F. Kennedy and concluded the Nassau Agreement. Penney continued as the government's advisor on arms control and participated in the preliminary discussion leading up to, and the signing of, the Partial Test Ban Treaty in Moscow in July 1963. Nuclear development was transferred from the Ministry of Supply (MoS) to the newly formed United Kingdom Atomic Energy Authority (UKAEA). Penney became a member of the UKAEA Board in 1954, and he chaired its official inquiry in the 1957 Windscale fire. When Sir John Cockcroft left in 1959 to become the master of Churchill College, Cambridge, Penney succeeded him as the Member for Scientific Research. He became deputy chairman in 1961 and chairman in 1964. The UKAEA had a difficult working relationship with the Central Electricity Generating Board (CEGB). Penney's management style was to avoid confrontation and seek consensus whenever possible, and the role of the UKAEA in the nuclear power industry was an advisory one. He endorsed the CEGB's 1966 decision to develop the Advanced Gas-cooled Reactor. He took the decision to proceed with the Prototype Fast Reactor at Dounreay and to upgrade the uranium enrichment plant at Capenhurst. Imperial College Penney was Rector of Imperial College London from 1967 to 1973. The job was far more trying than he anticipated, and there was no time for personal research. The university sector had expanded rapidly in the 1960s, and there were many personnel and financial difficulties to contend with. There was staff and student unrest that he had to deal with. Penney agreed to have student observers on the Board of Studies, and he brokered deals with the Association of University Teachers. Imperial College now had direct access to University Grants Committee funding and was no longer dependent on the University of London but money was still tight. Careful financial management created a surplus of income over expenditure. The college named the William Penney Laboratory at the South Kensington campus, which opened in 1988, in his honour. He served as the first chairman of the UK's Standing Committee on Structural Safety from 1976 to