William Penney, Baron Penney, Gibraltar-born English mathematician, physicist, and academic (b. 1909)
William George Penney, Baron Penney, (24 June 1909 – 3 March 1991) was an English mathematician and professor of mathematical physics at the Imperial College London and later the rector of Imperial College. He had a leading role in the development of Britain's nuclear programme, a clandestine programme started in 1942 during World War II which produced the first British atomic bomb in 1952.As the head of the British delegation working in the Manhattan Project, Penney initially carried out calculations to predict the damage effects generated by the blast wave of an atomic bomb. Upon returning home, Penney directed Britain's own nuclear weapons directorate, codename Tube Alloys, and directed scientific research at the Atomic Energy Research Establishment which resulted in the first detonation of a British nuclear bomb, (codename Operation Hurricane) in 1952.

After the test, Penney became chief adviser to the newly created British government's United Kingdom Atomic Energy Authority (UKAEA). He was later chairman of the authority, which he used in international negotiations to control nuclear testing with the Partial Nuclear Test Ban Treaty.

Penney's notable scientific contributions included the mathematics for complex wave dynamics, both in shock and gravity waves, proposing optimisation problems and solutions in hydrodynamics (which plays a major role in materials science and metallurgy.) During his later years, Penney lectured in mathematics and physics, and was the Rector of Imperial College London 1967–1973.