John Douglas Cockcroft (1897-1967) was an English physicist. His main contribution to physics consisted in designing a linear accelerator capable of giving such a speed to charged particles as to produce the transmutation of atomic nuclei.

John Cockcroft was born in Todmorden, Lancashire, on May 27, 1897. He attended the University of Manchester, where he studied mathematics under Horace Lamb in 1914-1915. Following service with the Royal Field Artillery in World War I, Cockcroft joined Metropolitan-Vickers, an engineering company, which sent him back to the University of Manchester to study electrical engineering. He transferred to St. John's College, Cambridge, where he took honors in mathematics in 1924.

Cockcroft was one of the gifted young physicists whom Ernest Rutherford gathered at the Cavendish Laboratory. By 1928 Cockcroft was at work on the problem of accelerating protons by high voltages, a task in which he was greatly helped by E.T.S. Walton. At...