Harold Melvin Agnew (March 28, 1921 – September 29, 2013) was an American physicist, best known for having flown as a scientific observer on the Hiroshima bombing mission and, later, as the third director of the Los Alamos National Laboratory.

He also served as a Democratic New Mexico State Senator from 1955 to 1961, and was the Scientific Adviser to the NATO Supreme Allied Commander Europe (SACEUR) from 1961 to 1964.

He was director of the Los Alamos National Laboratory from 1970 to 1979, when he resigned to become President and Chief Executive Officer of General Atomics.

The parts were shipped to New Mexico, where Agnew and Beverly met up with them, and rode the trucks hauling them to the Los Alamos Laboratory.

With Alvarez and Lawrence H. Johnston, Agnew had devised a method for measuring the yield of the nuclear blast by dropping pressure gauges on parachutes and telemetering the readings back to the plane.

[11] During the atomic bombing of Hiroshima, on August 6, 1945, Agnew, along with Alvarez and Johnston, flew as a scientific observer in The Great Artiste, piloted by Charles Sweeney, which tailed the Enola Gay as the instrumentation aircraft.

Agnew later recalled, "After we dropped our gauges I remember we made a sharp turn to the right so that we would not get caught in the blast – but we still got badly shaken up by it."

[15] Fellow postgraduate students at Chicago at the time included Tsung-Dao Lee, Chen Ning Yang, Owen Chamberlain and Jack Steinberger.

[14] With his doctorate in hand, Agnew returned to Los Alamos as a National Research Foundation Fellow, and worked on weapons development in the Physics Division.

[23] Under his directorship, Los Alamos developed an underground test containment program, completed its Meson Physics Facility, acquired the first Cray supercomputer, and trained the first class of International Atomic Energy Agency inspectors.

[23] In 1979, Agnew resigned from Los Alamos and became President and Chief Executive Officer of General Atomics, a position he held until 1985.

[13] In his letter of resignation to David S. Saxon, the President of the University of California, Agnew wrote that his decision was influenced by "dissatisfaction with University administration policies and a lack of advocacy for the total LASL [Los Alamos Scientific Laboratory] program" and "frustration with what I consider to be a continuing inequitable distribution of defense program funding by the Department of Energy between the LASL and LLL [Lawrence Livermore Laboratory].

"[25] Agnew chaired the General Advisory Committee of the Arms Control and Disarmament Agency from 1974 to 1978, and served as a White House science councillor from 1982 to 1989.

[28] In a 1977 article for the Bulletin of the Atomic Scientists, Agnew argued that the fusion reactions of neutron bombs could provide "tactical" advantages over conventional fission weapons, especially in countering the "massive armor component possessed by the Eastern bloc."

Citing conclusions reached by the Rand Corporation, Agnew argued that without affecting the armor of a tank, the neutrons produced by a fusion blast would penetrate the vehicle and "in a matter of a few tens of minutes to hours kill or make the crew completely ineffective."

Because the neutron bomb reduced collateral damage, it could be used in a much more selective fashion than a fission weapon, thereby providing a clear "advantage for the military defender as well as for the nearby non-combatant.

[6] Agnew was diagnosed with chronic lymphocytic leukemia, and died at his home in Solana Beach, California, on September 29, 2013, while watching football on television.