Newly discovered wartime documents have exposed the inner workings of a Japanese poison gas bomb factory during World War II, offering documentary evidence of chemical weapons production, worker injuries, and a militarist state that systematically subordinated society to its war machine. The records were uncovered at Japan's National Archives by historian Seiya Matsuno of the International Peace Research Institute of Meiji Gakuin University.

What the Documents Reveal

The central document, titled 'Compilation of Reports on the Implementation of Military Mobilisation,' is a production report covering fiscal 1941 operations at the Sone Manufacturing Plant of the Tokyo Second Army Arsenal. Matsuno analysed the material and published his findings in the June 2026 issue of the Japanese magazine Sekai.

The Sone plant, formerly located in Kitakyushu City in Fukuoka Prefecture, was responsible for filling artillery shells with toxic chemical agents and assembling poison gas bombs. The facility also manufactured smoke shells and incendiary bombs, according to the records.

Worker Accidents and Human Cost

The documents detail accidents that occurred during poison gas bomb production and the injuries suffered by workers on the factory floor. Until now, such incidents had been known almost exclusively through testimonies from former employees. These newly discovered records provide the first documentary corroboration of those survivor accounts, lending them fresh evidentiary weight.

Wartime Expansion and the Militarist System

According to Matsuno's research, the Sone plant expanded its workforce and boosted output during fiscal 1941 — a period when Japan was simultaneously prosecuting its war in China, preparing for a possible conflict with the Soviet Union, and planning military expansion into Southeast Asia. The records illustrate how production targets were driven by an escalating multi-front strategic calculus.

Matsuno emphasised that the Japanese military's deployment of chemical weapons in China and elsewhere violated international law. He further noted that the military conducted human experiments and committed other war crimes, which he described as reflecting the brutal character of Japan's wartime aggression. Under militarist rule, dissenting voices were systematically suppressed as the country became increasingly consumed by war fervour, he said.

Why This Matters for Historical Memory

Matsuno stressed that uncovering the realities of wartime history is essential to preventing similar tragedies from recurring. He argued that understanding how Japan became a country that inflicted serious harm on many Asian nations — and examining the conditions that enabled such developments — remains an important and unfinished task for contemporary Japanese society. The newly unearthed records add a rare layer of official documentation to a chapter of history that has often relied on oral testimony alone.

The findings come as debates over wartime accountability and historical memory continue to surface across East Asia, and as archival research increasingly challenges official narratives with primary-source evidence.