Toyokawa Naval Arsenal The was a major production facility for aviation ordnance , light arms , and ammunitions for the Imperial Japanese Navy during World War II . It was located in what is now part of the city of Toyokawa , Aichi Prefecture , Japan . It was one of the largest armaments plant in the Empire of Japan , but was not bombed by Allied forces until after the bombing of Hiroshima in World War II . History . Plans to establish the Toyokawa Navy Arsenal were made in March 1937 , along with the Suzuka Navy Arsenal in Mie Prefecture initially for the purpose of supplying 13 mm and 20 mm auto - cannons for the rapidly expanding Imperial Japanese Navy Air Service . The land was acquired in the towns of Toyokawa and Uchikubo ] and village of Yawata in eastern Aichi Prefecture by July 1938 , and construction began on October 1 , 1938 . The formal opening ceremony for the new facility was held on December 15 , 1939 . The new plant initially covered 200 hectares , and had 1500 employees . However , as the Second Sino - Japanese War quickly evolved into World War II , the demand for arms and ammunition increased . The Toyokawa Naval Arsenal expanded its facilities to 330 hectares in 1940 . The northern 60 percent was devoted to the production of gunpowder and ammunition , and the southern 40 percent of the area was devoted to machining and assembly work , especially for the Type 92 7 . 7 mm aircraft gun and the Type 99 20mm aircraft cannon . In addition to aircraft weapons , the Toyokawa Navy Arsenal also produced " guntō " Japanese swords , bayonets , the Nambu pistol and a variety of small caliber artillery weapons as well as optical equipment such as rangefinders and binoculars . By February 1945 , the plant employed 56 , 400 workers , including over 6000 school children who had been conscripted into working at the plant by the Japanese military . The plant also included its own water and gas facilities and dormitories for workers . Despite its obvious military significance , the Toyokawa Navy Arsenal was not bombed until the very last stages of World War II . On the morning of 7 August 1945 , 135 B - 29 Superfortress bombers of the USAAF 20th Air Force , 58th 73rd , 313th , and 314th Bombardment Wing s launched from Guam , Saipan and Tinian . They were joined by 48 P - 51 Mustang escort fighters deployed from Iwo Jima . Arriving over the target area at 10 : 13 AM , twelve B - 29s bombed the Toyokawa Naval Arsenal , while the remaining bombers concentrated on Toyokawa ’ s civilian population center , and the P - 51 strafed targets of opportunity . A total of 3 , 256 500 - lb bombs ( 813 tons ) was dropped on city from an altitude of 15 , 000 – 17 , 000 feet . Civilian casualties estimates range from 2 , 544 to 2 , 677 people killed , including several hundred women and 452 schoolchildren , who had been conscripted to work at the Toyokawa Navy Arsenal by the Japanese military . After World War II , the site of the former Toyokawa Navy Arsenal was developed into a large industrial complex , with a small portion given over to the JGSDF Camp Toyokawa . A large railway carriage factory operated by the Japan National Railway ( JNR ) is currently operated by Nippon Sharyo , and several other industries also operate on the site .