Sir John Douglas Cockcroft (27 May 1897 – 18 September 1967) was an English physicist who shared the 1951 Nobel Prize in Physics with Ernest Walton for their splitting of the atomic nucleus, which was instrumental in the development of nuclear power.

After service on the Western Front with the Royal Field Artillery during the Great War, Cockcroft studied electrical engineering at Manchester Municipal College of Technology whilst he was an apprentice at Metropolitan Vickers Trafford Park and was also a member of their research staff.

Later in the war, the fruits of the Tizard Mission came back to Britain in the form of the SCR-584 radar set and the proximity fuze, which were used to help defeat the V-1 flying bomb.

After the war Cockcroft became the director of the Atomic Energy Research Establishment (AERE) at Harwell, where the low-powered, graphite-moderated GLEEP became the first nuclear reactor to operate in western Europe when it was started on 15 August 1947.

In 1914, he won a County Major Scholarship, West Riding of Yorkshire, to the Victoria University of Manchester, where he studied mathematics.

They subsequently had four daughters, Joan Dorothea (Thea), Jocelyn, Elisabeth Fielden and Catherine Helena; and another son, Christopher Hugh John.

[4] Under Rutherford's supervision, he wrote his doctoral thesis "On phenomena occurring in the condensation of molecular streams on surfaces",[12] which was published in the Proceedings of the Royal Society.

[14] During this time he was an assistant to the Russian physicist Peter Kapitza, who was working on the physics of magnetic fields in extremely low temperatures.

The college gatehouse had to be partly taken down in order to repair damage done by deathwatch beetles, and Cockcroft supervised rewiring of the electrics.

Rutherford baulked at the price tag, but a £250,000 gift from Lord Austin enabled a 36-inch (910 mm) cyclotron, based on Lawrence's design, to be built, along with a new wing to house it.

[31] At the outbreak of the Second World War, Cockcroft took up the post of Assistant Director of Scientific Research in the Ministry of Supply, working on radar.

In 1938, Sir Henry Tizard showed Cockcroft Chain Home, the ring of coastal early warning radar stations built by the Royal Air Force (RAF) to detect and track aircraft.

[33] In April 1940, along he became a member of the Committee for the Scientific Study of Air Warfare formed to handle issues arising from the Frisch–Peierls memorandum, which calculated that an atomic bomb could be technically feasible.

Because Britain had developed many new technologies but lacked the industrial capacity to fully exploit them, it was decided to share them with the United States, although that nation was not yet at war.

The shared technology included radar technologies, in particular the greatly improved cavity magnetron designed by Oliphant's group at Birmingham, which the American historian James Phinney Baxter III described as "the most valuable cargo ever brought to our shores",[36] the design for the proximity fuze, details of Frank Whittle's jet engine and the Frisch–Peierls memorandum describing the feasibility of an atomic bomb.

Though these may be considered the most significant, many other items were also transported, including designs for rockets, superchargers, gunsights and submarine detection devices.

[35] Soon after his return, Cockcroft was appointed Chief Superintendent of the Air Defence Research Development Establishment (ADRDE) at Christchurch, Hampshire.

[38] Plans were given to the Americans by the Tizard Mission, but work continued in Britain, where a team was established at Christchurch under Charles Drummond Ellis in February 1942.

On a visit to the United States in November 1943, Cockcroft discussed adapting the American proximity fuze for British use with Merle Tuve.

[41] A sticking point was the director of the Montreal Laboratory, Hans von Halban, who was a poor administrator, did not work well with the Canadians,[42] and was regarded as a security risk by the Americans.

[50] Cockcroft was shocked when he was informed on 10 September 1945 that the British physicist Alan Nunn May, who worked at the Chalk River Laboratories, was a Soviet spy.

In August 1947, Cockcroft was one of the scientists who signed a petition urging that Nunn May's ten-year prison sentence be reduced, an act he later regretted.

[54] The low-powered, graphite-moderated GLEEP, which stood for Graphite Low Energy Experimental Pile, was designed by the Montreal Laboratory, and became the first nuclear reactor to operate in Western Europe when it was started on 15 August 1947.

[59] Under Cockcroft's direction, AERE took part in frontier fusion research in the post-war years, including the ZETA program.

James L. Tuck's group at the Los Alamos Laboratory was also researching fusion, and Cockcroft struck an agreement with the Americans that they would release their results together, which was done in 1958.

[60] As director of the AERE, Cockcroft famously insisted that the chimney stacks of the Windscale plutonium production reactors be fitted, at great expense, with high-performance filters.

A 1961 plan to build it at the entrance to the college, as was traditional at Cambridge, led to the immediate resignation of Francis Crick, a staunch atheist, as a fellow.

He served as chancellor of the Australian National University in Canberra from 1961 to 1965, a largely symbolic post that involved a visit once a year for degree conferring ceremonies.

[4] In addition to winning, along with Walton, the Hughes Medal and 1951 Nobel Prize in Physics, Cockcroft received numerous awards and accolades over the years.

They include his lab books, correspondence, photographs (with dozens depicting the construction of Chalk River, CKFT 26/4), theses and political papers.