The arsenal opened its doors in 1871, just three years after the Meiji Restoration toppled the shogunate and thrust Japan into a crash course in Western industrialization. Its mission was urgent: build modern weapons so Japan would never be vulnerable to the colonial powers encircling Asia. The facility's first great achievement was the Murata rifle, designed by Major Murata Tsuneyoshi, which became the first rifle produced entirely in Japan. Between 1880 and 1886, workers manufactured between 60,000 and 70,000 of these weapons using machinery supplied by the Winchester Company from the United States. By 1893, the arsenal's output had reached a relentless pace of 200 rifles and 200,000 cartridges per day. The compound also produced the Arisaka rifle that would become standard issue for the Imperial Japanese Army, along with licensed Mauser-style rifles based on the Gewehr 98, exported to the military of Siam.

After World War I, the arsenal expanded beyond small arms into aircraft production. Japanese army planes rolled off the factory floor, and in a remarkable diplomatic arrangement, the Imperial Russian Army placed an order for 10 aircraft before 1916, well before the Russian Revolution would end such partnerships. The facility also became a center for military science. The Imperial Japanese Army Institute of Science was established within its walls, and in 1937, the secretive Number Nine Research Laboratory broke off as an independent unit. Yet the arsenal's very success bred friction on the factory floor. Discipline was notoriously strict, and Koishikawa became a flashpoint for Japan's early labor movement, with workers organizing some of the country's first major industrial disputes.

At 11:58 on the morning of September 1, 1923, the Great Kanto earthquake struck the Tokyo-Yokohama region with a magnitude of 7.9. The arsenal suffered devastating damage. Red-brick buildings that had stood since the 1870s crumbled, machinery was wrecked, and fires raged through the compound. The government calculated that complete reconstruction would be prohibitively expensive. For over a decade the facility limped along in its damaged state, until the decision was finally made in October 1935 to relocate operations to Kokura in Kyushu, some 900 kilometers to the southwest. After 66 years, the sounds of hammers and cartridge presses fell silent in Koishikawa.

The abandoned arsenal grounds found new purpose remarkably quickly. In 1937, just two years after the military vacated, Korakuen Stadium opened on the site as Japan's first purpose-built baseball venue. The Yomiuri Giants began calling it home in 1938, and for half a century the stadium hosted some of the most storied moments in Japanese baseball. In 1988, the inflatable white roof of the Tokyo Dome replaced the open-air ballpark, and the surrounding area blossomed into Tokyo Dome City, a sprawling entertainment complex with roller coasters, a natural hot spring spa, hotels, and restaurants. Adjacent to the complex, the Koishikawa Korakuen Garden preserves a fragment of the original Mito Domain estate that predated even the arsenal, connecting a thread of green tranquility back through the centuries of transformation.