The plans for the Toyokawa Naval Arsenal were drawn up in March 1937, alongside the Suzuka Naval Arsenal in neighboring Mie Prefecture. Japan was already fighting in China, and the Imperial Japanese Navy Air Service needed 13mm and 20mm auto-cannons at a pace existing factories could not sustain. Land was acquired in the towns of Toyokawa and Uchikubo and the village of Yawata by July 1938. Construction began on October 1 of that year, and the facility formally opened on December 15, 1939, covering 200 hectares with an initial workforce of 1,500. The Second Sino-Japanese War was already escalating toward a wider Pacific conflict. By 1940, the arsenal had expanded to 330 hectares -- the northern section devoted to gunpowder and ammunition production, the southern section to machining and assembly.

The Toyokawa Naval Arsenal's primary output was aircraft weaponry: the Type 92 7.7mm aircraft machine gun and the Type 99 20mm cannon, workhorses of the Japanese naval air fleet. But the plant's capabilities extended beyond firearms. Workers also produced optical instruments -- rangefinders and binoculars essential for naval gunnery and aerial observation. The facility was self-contained, with its own water treatment and gas generation plants and dormitories for the workforce. By February 1945, the number of workers had swollen to 56,400. Among them were over 6,000 school-age children, conscripted by the Japanese military to fill the labor shortages that plagued the empire in its final year. These children worked alongside adults on the production lines, assembling the weapons of a war that was already lost.

Despite its obvious strategic importance, the Toyokawa Naval Arsenal remained unbombed through years of escalating Allied air campaigns. That reprieve ended on the morning of August 7, 1945. One hundred thirty-five B-29 Superfortress bombers from the USAAF 20th Air Force -- drawn from the 58th, 73rd, 313th, and 314th Bombardment Wings -- launched from the Pacific island bases of Guam, Saipan, and Tinian. Forty-eight P-51 Mustang fighters deployed from Iwo Jima flew escort. The formation reached Toyokawa at 10:13 AM. Twelve B-29s targeted the arsenal itself, while the remaining bombers struck the surrounding civilian population center. The P-51s strafed targets of opportunity at low altitude. In total, 3,256 500-pound bombs rained down -- 813 tons of high explosives dropped from 15,000 to 17,000 feet. The casualty toll was devastating: between 2,544 and 2,677 people killed, including several hundred women and 452 schoolchildren who had been compelled to work at the very facility that made it a target.

After Japan's surrender, the shattered arsenal did not become a memorial or a monument. It became an industrial park. The massive footprint that once produced naval armaments was subdivided among new tenants. A portion was allocated to JGSDF Camp Toyokawa, maintaining a military presence on the site. The largest civilian operation was a railway carriage factory initially run by Japan National Railways, which today operates under Nippon Sharyo, one of Japan's leading manufacturers of rolling stock -- including components for the Shinkansen bullet train network. Other industries moved in alongside, and the site gradually transformed from a ruin of war into an engine of peacetime commerce. The conversion is so thorough that little visible evidence of the arsenal remains on the surface.

The Toyokawa Naval Arsenal's story resists simple summary. It is a story of industrial ambition and military overreach, of wartime production that consumed even children in its machinery. The bombing came just one day after Hiroshima, part of the ferocious final campaign that preceded Japan's surrender on August 15, 1945. The 452 schoolchildren who died at Toyokawa represent one of the war's quieter tragedies -- young lives pressed into factory service by a government that had run out of adult workers and was running out of time. Today, the factories and barracks that occupy the old arsenal grounds hum with civilian industry, but the memory of what happened here on that August morning persists in local commemorations and the city's historical record.