The Battle of Okazaki was a major battle of the Boshin War which was fought between the pro-Imperial Choshu Domain and the pro-Shogunate Nagaoka Domain in Mikawa Province, Japan in January 1867. The battle marked the first showdown between the vanguards of the Imperial and Shogunate factions, and Choshu captured Okazaki and the rest of Mikawa Province after separately defeating the garrison of Okazaki and Tokugawa Hisakane's nearby army.
Background[]
The fall of Nagoya to the pro-Imperial Choshu Domain in December 1866 marked the end of an early phase of the Boshin War as the Choshu Domain, recently appointed the vanguard of Emperor Meiji's Imperial armies, vanquished its main rival in the Kansai region, only to be confronted with a new alliance of foes. Choshu's ascendancy to the head of the Imperial cause led to Mori Takachika making enemies with the Tokugawa Shogunate's vanguard, the massive Nagaoka Domain of central Honshu, as well as the powerful Kanazawa Domain of north-central Honshu and the Wakayama Domain of present-day Wakayama Prefecture in southern Kansai.
While the Wakayama Domain was preoccupied with invading Yamato Province and conquering the pro-Imperial Takatori Domain and the Kanazawa Domain was embattled in northern Honshu, the Nagaoka Domain - engaged in both north and south-central Honshu - mobilized several of its armies in Mikawa Province, to the south of Owari Province, captured by Choshu with the fall of Nagoya. Takachika decided to prioritize the defeat of Nagaoka in the south in order to buy the Choshu Domain enough time to bring in reinforcements from Chugoku and Osaka to crush Wakayama in the south, so he led his 1,890-strong army south from Nagoya to invade Mikawa Province. His goal was to destroy the two Nagaoka armies, led by Tokugawa Hisakane and Sannomiya Toshitsuna, who were encamped near the historic castle of Okazaki. Takachika opted to attack Okazaki, anticipating that the Nagaoka armies would come to the castle's aid.
Battle[]
The main battle at Okazaki
Takachika deployed his army outside of Okazaki Castle, and he soon received word that Hisakane's army was coming to garrison commander Kikuchi Yukiyasu's aid. Counting on Yukiyasu to remain holed up in the castle with his poorly-armed garrison, Takachika marched his army to face off against Hisakane's reinforcements before they could cross the Oto River to join forces with the undermanned garrison. His army intercepted Hisakane's army just before its forward units could cross the river to the castle's side, and Takachika had his right-flank line infantry array themselves to outflank the Nagaoka reinforcements. In the ensuing battle, the Nagaoka army was slaughtered from multiple sides, and it quickly collapsed under heavy gunfire. Takachika sent his cavalry to give chase, massacring hundreds of fleeing Nagaoka soldiers.
Choshu's assault on Okazaki Castle
With Hisakane's army defeated, Takachika refocused his army on capturing Okazaki Castle itself. As predicted, Yukiyasu and his garrison made no effort to rescue their wavering comrades, and the castle was thus cut off from any aid. A Nagaoka fleet in Ise Bay attempted to provide naval support to the defenders, but their shells missed the Choshu army entirely. The Choshu army proceeded to assault Okazaki Castle from three sides, scaling the walls and firing on the overwhelmed defenders from behind after making it around them. The defenders put up stiff resistance in spite of their outdated armaments, but their valor was in vain, as the Choshu army overwhelmed any resistance offered to them. Choshu captured Okazaki with 357 losses, while Nagaoka suffered much heavier losses; they not only lost their garrison, but also a significant portion of Hisakane's army.
Aftermath[]
Hisakane's army survived its defeat at Okazaki, retreating to the Chita Peninsula; Sannomiya Toshitsuna's army was untouched by the battle at Okazaki, enabling the two Nagaoka armies to retreat in good order. However, the Nagaoka fleet in Ise Bay withdrew, leaving the two Nagaoka armies stranded on the peninsula. While they managed to outmaneuver Takachika's preoccupied Choshu army for a month, they were ultimatley annihilated at the Battle of Chita a month later.
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