The Japanese 17th Area Army was formed on January 22, 1945 under the Imperial General Headquarters as the successor to the Chosen Army of Japan as part of the last desperate defense effort by the Empire of Japan to deter possible landings of Allied forces on the Korean peninsula during Operation Downfall (or Operation Ketsugō (決号作戦,Ketsugō sakusen?) in Japanese terminology). It was headquartered in Keijō. However, the actual administrative structure of the former Chosen Army remained in place, and thus the leadership of the 17th Area Army concurrently held the equivalent posts within the Chosen Army, which was also called the Korean District Army.
As with the field armies raised on the Japanese home islands it consisted mostly of poorly trained reservists, conscripted students and home guard militia, as most of the veteran, trained troops of the Chosen Army had already been transferred to other fronts in the Pacific War. In addition, the Japanese had organized the Patriotic Citizens Fighting Corps — which included all healthy men aged 15–60 and women 17–40 — to perform combat support, and ultimately combat jobs. Weapons, training, and uniforms were generally lacking: some men were armed with nothing better than muzzle-loading muskets, longbows, or bamboo spears; nevertheless, they were expected to make do with what they had.
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