By 1944, the atomic bomb was no longer mainly a question of whether nuclear fission released extraordinary energy. That question had been answered. The harder question was whether a civilisation-scale system could turn fissile material into a device that worked on command.
This ninth segment begins with an inherited world already transformed by Chicago Pile-1, Oak Ridge, Hanford and Los Alamos. Nuclear chain reactions had been demonstrated. Enrichment plants and reactors were being built. Yet the final route to a plutonium weapon remained uncertain.
The inherited world: production without a finished weapon
Oak Ridge pursued several uranium-enrichment technologies in parallel. Hanford was designed to manufacture plutonium on an industrial scale. Los Alamos had the task of turning these extraordinary materials into weapons. The project therefore depended on handoffs: mines and mills supplied uranium; factories transformed and separated materials; reactors created plutonium; laboratories measured its properties; engineers and machinists translated those properties into hardware.
The National Park Service notes that by mid-1944 two basic weapon models had emerged: a gun-type uranium weapon and a plutonium implosion weapon. The uranium design was comparatively direct. The plutonium route became much more difficult.
Why plutonium changed the design problem
Reactor-produced plutonium contained isotopic characteristics that made a simple gun-type assembly unsuitable. The risk of premature initiation was too high. Los Alamos therefore had to make implosion work: use chemical explosives arranged around a plutonium core so that the inward-moving shock compressed it rapidly and symmetrically.
This was a striking convergence of histories. Nuclear physics supplied the reason for compression. Metallurgy supplied a workable core. Precision machining supplied geometry. Electrical timing and detonators supplied coordination. High explosives supplied the mechanical force. Diagnostics supplied evidence about whether the compression was actually occurring as intended.
The nuclear age depended, at its final approach, on making ordinary chemical explosives behave with extraordinary precision.
Hanford hands material to Los Alamos
Hanford’s B Reactor reached criticality in September 1944 and moved toward full production. Its purpose was not to make a bomb at the reactor site. It produced plutonium that then had to be chemically separated, purified, transported and studied elsewhere. Material became information; information changed design; design changed manufacturing.
This is why the final year cannot be understood as a single laboratory story. The device that would be tested at Trinity embodied successful transfers between distant institutions. If any major link failed—reactor operation, chemical separation, transport, metallurgy, explosive timing, measurement—the final test could not simply proceed unchanged.
Testing pieces of the problem
Los Alamos conducted repeated experiments on implosion, detonators, explosive lenses and diagnostic techniques. The challenge was not merely to create a large explosion. It was to shape a rapidly moving pressure wave with enough symmetry to compress the core in the required way.
That requirement rewarded a different kind of knowledge from the theoretical breakthroughs earlier in the story. The decisive questions were now practical: Can components be manufactured within tolerance? Can detonators fire closely enough together? Can the shock front be measured? Can the metal core be fabricated safely? Can the system survive transport and assembly?
What still did not exist
Even in early 1945, one thing remained absent: empirical proof that the complete plutonium implosion system would produce a nuclear explosion. The project had calculations, component tests, increasingly mature designs and growing quantities of material. It did not yet have the answer supplied by a full-scale test.
That absence defines the pressure pushing this interval forward. By the summer of 1945, the separate roads had narrowed into a single question in the New Mexico desert.
Previous in the tube: Part 8: 1942–1944 — Nuclear Physics Becomes Industry.
Next in the tube
The next and final segment follows the last handoff from engineered expectation to observed reality: Part 10: July 16, 1945 — When the World Changed State.