Todmorden, in Lancashire, had been the home of the Cockroft family for more than 400 years when John was born there on May 27, 1897. The Cockrofts had been involved in the weaving and cotton-manufacturing process for most of that time. Young John attended local schools in Todmorden and then entered the University of Manchester in 1914. Within a year, however, he left school to join the Royal Field Artillery in World War I.

After the war, Cockroft became an apprentice at the Metropolitan Vickers Electric Company. He then enrolled at St. John's College, Cambridge, where he earned his bachelor's degree in 1924. Four years later, he received his doctorate from Cambridge.

While working with Ernest Rutherford at Cambridge, Cockroft became interested in the artificial transmutation of the atomic nucleus. Rutherford had experienced some success in this kind of research using alpha particle s from naturally radioactive materials. In 1919, for example, he had...