Witnessed nuclear capabilities from the beginning
NUCLEAR PIONEER
28-3-1921 - 29-9-2013
Harold Agnew, the last surviving major figure to have been present at the birth of the nuclear age - who helped build the world's first reactor and atomic bombs, flew on the first atomic strike against Japan, filmed the mushroom cloud, helped perfect the hydrogen bomb and led the Los Alamos National Laboratory at the height of the Cold War - has died at his home in Solana Beach, California. He was 92.
Harold Melvin Agnew was born in Denver, Colorado, on March 28, 1921, the only child of a stonecutter of Scots-Irish heritage. He majored in chemistry at Denver University, graduated in 1942 and won a scholarship to Yale.
But the secret wartime effort to build an atomic bomb intruded on his studies. Early in 1942 he was assigned to Enrico Fermi, the Italian Nobel laureate who was helping to lead the project at the University of Chicago. Agnew did what he called "grunt work", making scientific measurements and getting a hefty dose of radiation. Redirected because of the health danger, he helped stack tonnes of graphite bricks and uranium into a pile at a university squash court.
On December 2, 1942, Agnew and a few dozen others gathered to see if the pile could sustain a chain reaction. Recording pens jumped as atoms split in two. The success meant that, in theory, the human race now had the means to illuminate cities or level them. He was 21.
Agnew arrived at Los Alamos in March 1943 with his wife, Beverly. He helped build and run a particle accelerator whose data helped demonstrate the merits of various bomb designs.
When the world's first nuclear blast lit up the New Mexico desert before dawn on July 16, 1945, Agnew was already far away, preparing for the bombing of Hiroshima.
On August 6, he boarded a B-29 bomber that accompanied the Enola Gay, which was carrying the bomb codenamed "Little Boy." Agnew and two other scientists measured the size of the shock wave and thus the bomb's power.
Afterwards, he and his colleagues took turns peering out a small window at the mushroom cloud and the ground damage. Agnew filmed the devastation with a 16-millimetre movie camera he had taken along. He was the only person to witness the whole undertaking, from reactor to weapon to Hiroshima.
After the war, he studied with Fermi at Chicago and received his PhD in physics in 1949. Returning to Los Alamos, he joined the hunt for a technical edge over the Soviet Union. The first hydrogen bomb, tested successfully in 1952, weighed a staggering 60 tonnes. Agnew helped perfect lighter H-bombs that were deliverable over long distances.
He is survived by a daughter, a son, four grandchildren and three great-grandchildren. New York Times
Frequently Asked Questions about this Article…
Harold Agnew (28 March 1921 – 29 September 2013) was a physicist who helped build the world’s first nuclear reactor and played direct roles in early atomic weapons development. He flew on the Hiroshima mission, filmed the mushroom cloud, helped perfect deliverable hydrogen bombs and led the Los Alamos National Laboratory at the height of the Cold War — earning him the description of a nuclear pioneer.
As a young scientist assigned to Enrico Fermi in 1942, Agnew helped stack tonnes of graphite bricks and uranium into a pile on a university squash court. On 2 December 1942 he and colleagues recorded the first sustained chain reaction, demonstrating the physics that underpins both nuclear power and nuclear weapons.
On 6 August 1945 Agnew boarded a B-29 that accompanied the Enola Gay. He and two other scientists measured the shock wave to estimate the bomb’s power, and Agnew filmed the mushroom cloud with a 16mm camera. He was noted as the only person to have witnessed the whole process from reactor to weapon to Hiroshima.
Agnew arrived at Los Alamos in March 1943 and helped build and run a particle accelerator whose data supported decisions about bomb designs. His wartime work contributed directly to the development and testing of the first nuclear weapons.
After the war Agnew earned a PhD in physics in 1949 studying with Enrico Fermi, returned to Los Alamos, and helped develop lighter, deliverable hydrogen bombs following the massive 1952 H-bomb tests. He later led the Los Alamos National Laboratory during the Cold War.
Agnew’s career spans the birth of the nuclear age — from the first chain reaction to wartime use and later hydrogen-bomb development. His work illustrates the dual-use nature of nuclear technology: the same physics can enable electricity generation or create devastating weapons, a central theme in nuclear history.
Agnew was born in Denver, Colorado, the son of a stonecutter, majored in chemistry at Denver University, won a scholarship to Yale, and later completed a PhD with Enrico Fermi. He died at his home in Solana Beach, California, aged 92, and is survived by a daughter, a son, four grandchildren and three great‑grandchildren.
Agnew’s story highlights how nuclear technology has long-term strategic importance and dual applications in energy and national security. For investors, that history underlines the sector’s technological complexity, regulatory sensitivity and geopolitical relevance — factors to consider when researching nuclear-related companies and policies.
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