Also known as: Kawagoe Night Battle (河越夜戦), Kawagoe Engagement (河越合戦)
The Battle of Kawagoe Castle was fought on May 19, 1546, in Musashi Province at and around Kawagoe Castle, held by the Houjou, against an overwhelming force led by Uesugi Norimasa (Yamanouchi-Uesugi Clan and the then-Kantou Kanrei), Uesugi Tomosada (Ougigayatsu-Uesugi Clan), and Ashikaga Haruuji (the then-Koga Kubou).
When the Uesugi-Ashikaga forces besieged Kawagoe Castle on Oct. 31, 1545, they numbered roughly 70,000-80,000 men to the 3,000 in the castle garrison, led by Houjou Tsunashige. (One account says that all the daimyo of the Kantou except Chiba Toshitane of Shimousa participated.) Ujiyasu led a reinforcement force of 8,000 from Sagami, and the fighting was locked in stalemate for several months. Kushima Tsunahiro (Tsunashige's younger brother), who was in Ujiyasu's reinforcement force, sent a single horseman to slip through the Uesugi-Ashikaga forces into the castle to coordinate a surprise attack.
Ujiyasu sent a false offer of surrender to the Uesugi army. Instead of accepting it, they attacked the Houjou fiercely. Ujiyasu pulled back, luring the enemy into believing they had the battle in hand. On the night of May 19, Ujiyasu split his 8,000 troops into four companies. One of them he left under the leadership of Tame Mototada with the command that it would not move until the end of the battle. Ujiyasu led the other three companies, traveling lightly without armor, into the enemy camp at midnight. The Uesugi-Ashikaga army collapsed in pandemonium. Uesugi Tomosada was killed. When Tame Mototada saw from behind Ujiyasu that he had thrust too far in, he sounded a conch shell to warn Ujiyasu and pull him back. On the other hand, Tsunashige, who had been watching over the battle from inside the castle, led his troops into Ashikaga Haruuji's army, shouting "We've won! We've won!" Occupied with Ujiyasu's army and completely unprepared, the Ashikaga army was routed. The total number of dead on the Uesugi-Ashikaga side reached 13,000 according to some accounts.
As a result of the battle, the Ougigayatsu-Uesugi Clan was destroyed, and Kantou Kanrei Uesugi Norimasa rapidly lost power and influence until he was driven out of Hirai Castle, his main stronghold, and forced to seek refuge with Nagao Kagetora in Echigo. Immediately thereafter, Ashikaga Haruuji was surrounded at the old imperial palace and forced to retired in favor of his son, Ashikaga Yoshiuji, whose wife was Houjou Ujiyasu's daughter.