Former IJA 5th Division Headquarters Site (Hiroshima Castle)

The former 5th Division Headquarters site (広島第五師団司令部跡) lies within the grounds of Hiroshima Castle (広島城, Hiroshima-jō) in Naka-ku, Hiroshima City. Known alternately as Carp Castle (鯉城, Rijō) for the carp that once filled its moats, Hiroshima Castle and the 5th Division together embody the city's identity as a "military capital" (軍都, gunto) from the Meiji era through the end of World War II — an identity that ended catastrophically with the atomic bombing on 6 August 1945.

Origins: From Hiroshima Garrison to 5th Division (1871–1888)

In December 1871 (Meiji 4), following the abolition of feudal domains, the new Meiji government stationed the First Detachment of the Chinzei Garrison (鎮西鎮台第一分営) on the grounds of Hiroshima Castle; in January 1873 it became the Hiroshima Garrison (広島鎮台, Hiroshima Chindai), one of six regional military commands. The garrison occupied the Honmaru (main bailey) and surrounding areas of the castle, which had served the Asano clan as domain lords during the Edo period. On 14 May 1888, as part of the army-wide reorganization from garrisons to divisions, the Hiroshima Garrison was redesignated as the 5th Division (第五師団, Dai-go Shidan). The division recruited troops primarily from Hiroshima, Shimane, and Yamaguchi prefectures in the Chūgoku region.

The Carp Division Nickname

The 5th Division's famous nickname "Koi Shidan" (鯉師団, Carp Division) derived from Hiroshima Castle's alternate name "Rijō" (鯉城, Carp Castle), itself named for the abundant carp in the castle's moats. The division's wartime unit code name (通称号) was "Koi" (鯉兵団, Koi Heidan). This connection between the castle and the carp would later give its name to Hiroshima's professional baseball team, the Hiroshima Toyo Carp.

Imperial General Headquarters at Hiroshima (1894–1895)

During the First Sino-Japanese War, Hiroshima's strategic importance was dramatically elevated. In September 1894, the Imperial General Headquarters (大本営, Daihon'ei) was relocated from Tokyo to the 5th Division headquarters building on the Honmaru of Hiroshima Castle — the only time in Japanese history the supreme military command center was moved outside the capital. Emperor Meiji himself took up residence there, and the Imperial Diet convened a special session in Hiroshima. The city served as the nerve center of Japan's war effort, with Ujina Port handling the embarkation of troops and supplies to the Korean and Chinese theaters. The wooden headquarters building where Emperor Meiji resided survived until 1945.

Major Campaigns: China, Russia, and China Again (1894–1941)

The 5th Division compiled a distinguished combat record across Japan's modern wars. In the First Sino-Japanese War (1894–95), elements fought in Korea and Manchuria. During the Russo-Japanese War (1904–05), the division fought at the Battles of Shaho, Heikoutai (Sandepu), and Mukden as part of the Fourth Army. In the Siberian Intervention, the division was deployed to the Russian Far East from 1919 to 1922.

During the Second Sino-Japanese War from 1937, the 5th Division was mobilized and deployed to North China, participating in operations across Chahar, Hebei, and Shanxi. The division fought in the Chahar Operation, the capture of Taiyuan, the Battle of Xuzhou, and other major engagements, and in September 1940 formed the main force of the occupation of northern French Indochina. The 5th Division was recognized as one of the IJA's premier combat divisions.

The Malaya Campaign and Fall of Singapore (1941–1942)

The 5th Division's most famous — and historically consequential — campaign came at the outset of the Pacific War. Assigned to Lieutenant General Yamashita Tomoyuki's 25th Army for Operation E (the invasion of Malaya), the division was one of three assault divisions (alongside the 18th Division from Kurume and the Imperial Guards Division).

On 8 December 1941, the 5th Division landed at Singora and Patani on the east coast of Thailand. Within days, it smashed through the British defensive positions at the Battle of Jitra (11–13 December 1941) in northern Malaya, capturing enormous quantities of supplies and shattering the myth of British impregnability. The division's troops, among them the Hiroshima-based 11th Infantry Regiment (歩兵第十一聯隊), became famous for their use of bicycles — soldiers pedaled rapidly down Malayan roads, outflanking retreating British and Commonwealth forces at a pace that earned the campaign the nickname "the Bicycle Blitzkrieg."

The 5th Division continued its advance through central Malaya, winning a decisive victory at the Battle of Slim River (7 January 1942) where tanks and infantry overran multiple British defensive lines in a single night attack, and capturing Kuala Lumpur on 11 January 1942. On the night of 8–9 February 1942, the 5th Division crossed the Johor Strait to assault Singapore Island from the northwest. After fierce fighting along Bukit Timah Road, the British garrison under Lieutenant General Arthur Percival surrendered unconditionally on 15 February 1942 — the largest capitulation in British military history, with approximately 80,000 troops taken prisoner.

Later War and Surrender (1942–1945)

After Singapore, the 5th Division was transferred to various rear-area duties. From 1943, it was stationed in the Dutch East Indies (primarily on Seram and other islands in the Moluccas) under the Second Area Army. The division remained in the eastern Dutch East Indies when the war ended in August 1945 and surrendered to Australian forces.

Hiroshima as Military Capital

Back in Hiroshima, the castle grounds hosted a vast military complex that extended well beyond the 5th Division headquarters. Facilities included the Hiroshima Army Weapons Depot, the Hiroshima Army Clothing Depot (被服支廠), military hospitals, barracks for multiple regiments, officer training schools, and the Chūgoku Regional Army command. After the 5th Division deployed overseas, the Reserve 5th Division (留守第五師団) and later the Hiroshima District Army command occupied the headquarters. In June 1945 the district command was reorganized as the Chūgoku Military District headquarters (中国軍管区司令部), based in the Honmaru. Field Marshal Hata Shunroku's Second General Army (第二総軍), which commanded the defense of all western Japan in preparation for the anticipated Allied invasion, had set up its headquarters in April 1945 outside the castle, in the former 5th Cavalry Regiment barracks at Futaba-no-sato beside the East Parade Ground.

Atomic Destruction: 6 August 1945

At 8:15 a.m. on 6 August 1945, the atomic bomb "Little Boy" detonated approximately 600 meters above central Hiroshima, roughly 900 meters south-southeast of the castle. The blast and thermal radiation instantly destroyed the entire castle complex: the wooden main tower (天守閣) that had survived since the 1590s, the Imperial General Headquarters building, all barracks and administrative structures, and the trees of the castle grounds were flattened. Soldiers and staff of the Chūgoku Military District headquarters and the other units stationed within the castle walls were killed in large numbers. The Chūgoku Regional Army's semi-underground communications bunker (中国軍管区司令部防空作戦室) was the only military structure to survive, and it transmitted the first report of the atomic bombing to Tokyo.

Reconstruction and Memorials

Hiroshima Castle's main tower was reconstructed in reinforced concrete in 1958, serving as a museum of the city's history. The Ninomaru (second bailey) gate and turrets were reconstructed in wood in 1994. On the Honmaru, the stone foundations of the Imperial General Headquarters building (大本営跡) are preserved as a memorial, with explanatory signage describing its history. Memorial stones and markers throughout the castle grounds commemorate the military units that were based there, including the 5th Division. The site serves as both a castle park and a solemn reminder of Hiroshima's military past and its destruction by the atomic bomb.

Today, the 5th Division headquarters site within Hiroshima Castle stands at the intersection of three historical narratives: the feudal castle heritage of the Mōri and Asano clans, the modern military history of one of the IJA's most formidable divisions, and the atomic tragedy that obliterated both the castle and the city around it.