Battle of Mihonoseki

美保関の合戦

Amago Revival Army

Izumo Province

Rebel Forces

Date:  Ninth month of Eiroku 12 (1569)

Location:  Mihonoseki in Izumo Province

Synopsis:  After initially aiding the Amago revival army to make landfall in Izumo Province, Oki Tamekiyo, the lord of Oki Province, suddenly rebelled against the Amago for reasons that remain uncertain.  Tamekiyo positioned his forces anticipating an attack by land, but Yamanaka Yukimori sailed with his army to enable a direct attack on the main camp, defeating Tamekiyo. 

Lord:  Amago Katsuhisa

Commanders:  Yamanaka Yukimori, Tachihara Hisatsuna

Forces:  Approximately 400

Losses:  Unknown

Commanders:  Oki Tamekiyo

Forces:  Between 400 and 1,000

Losses:  975 (+ Oki Tamekiyo committed seppuku to spare the lives of prisoners)

The Battle of Mihonoseki occurred in the ninth month of Eiroku 12 (1569).  This conflict was triggered by a rebellion led by Oki Tamekiyo against the Amago revival army led by Yamanaka Yukimori.  The battle is named after the place name where it occurred in Mihonoseki in Izumo Province.

Prelude

In 1569, the Amago revival army backed Amago Katsuhisa as the head of the clan and, after sailing from the island of Oki Province to the coast of Izumo Province, received the cooperation of Oki Tamekiyo to make landfall.  The Amago forces proceeded to attack assorted castles in Izumo, expanding their power by seizing control of nearly the entire province.  This event is known as the Invasion of Unshū by the Amago Revival Army.  Thereafter, during an assault against the main base of the Mōri in Izumo at Gassantoda Castle, the Mōri army from Iwami led by Hattori Sabei attempted to thwart the Amago, but were defeated in the Harate District in the Battle of Harate.

In the tenth month of 1569, after assisting the Amago revival army to make landfall in Izumo and allying with them in the Battle of Harate, Oki Tamekiyo suddenly rebelled.  The reasons for his rebellion are not certain, but, in an effort to subdue the rebellion, the Amago revival army including Yamanaka Yukimori and Tachihara Hisatsuna led forces to Mihonoseki.

Course of events

Oki Tamekiyo divided his forces into two camps, positioning the first camp in the vicinity of Manogagoku and the main camp near the Mihono Shrine.

Tamekiyo anticipated that the Amago revival army would attack by land from the Shimane Peninsula, so he positioned the first battalion in a location to counter them.

Meanwhile, as the leader of the Amago forces, Yamanaka Yukimori planned to thwart Tamekiyo’s strategy by crossing the sea and launching a surprise attack directly against the main camp of the rebels.  After assembling vessels in the harbor, the Amago soldiers sailed from Hakushū-Yonago across the sea to initiate their attack on the main base of Tamekiyo.

In the initial stages of the conflict, owing to their numerical superiority, the rebels overwhelmed the Amago revival army.  After being cornered, at one point the Amago confronted the prospect of annihilation, but, after the arrival of reinforcements including the Yokomichi brothers (Yokomichi Takamitsu and Yokomichi Takamune), along with Matsuda Masayasu and others, the situation on the battlefield reversed.  The army led by Oki Tamekiyo collapsed and was destroyed while Tamekiyo himself fled to his home of Oki Province.

The soldiers from the first camp positioned by Tamekiyo did not arrive in time to participate in the battle at the main camp.  After destroying the main camp, the Amago revival army captured and took prisoner the soldiers from the first camp.  Together with surviving troops from the main camp, a total of approximately 400 soldiers were taken to Daikon Island.  Upon the condition that Tamekiyo commit seppuku, their lives were spared and they were released.

Consequences

After the death of Tamekiyo, who had governed Oki, he was succeeded by his younger brother, Oki Kiyozane.  Kiyozane pledged cooperation with the Amago revival army, marking the end to the rebellion.  However, although the Amago revival army had subdued the rebellion, the fact that the conflict occurred between members of the same clan, it weakened the overall power of their army.

Around this time, the main division of the Mōri that had been on an expedition in Kyūshū departed Tachibanayama Castle in Chikuzen Province and commenced their return march with the aim of subduing the Ōuchi revival army and the Amago revival army.  Amano Takashige (who was holed-up in Gassantoda Castle) and other members of the Mōri army in Izumo successfully stalled for time until the return of the main division from Kyūshū.

Later, owing to resistance by Mōri forces in the Hinobori area in an event known as the Battle of Hinobori, the Amago revival army was unable to mount an assault against Gassantoda Castle serving as the main base of the Mōri in Izumo.  Instead, the Amago forces engaged in battle with the main division of the Mōri returning from Kyūshū at the Battle of Fubeyama.

Motivations for the rebellion by Oki Tamekiyo

The reasons why Oki Tamekiyo rebelled against the Amago revival army cannot be confirmed from authenticated sources.  One account provides reasons, but there are inconsistencies.  In another account, at the Battle of Harate, Tamekiyo felt it was unfair that his younger brother, Oki Kiyozane, received greater recognition than he did, after which he colluded with Amano Takashige, the lord of Gassantoda Castle, to launch the rebellion.  Another chronicle notes that he fought as a member of the Mōri army.  Finally, there is a story that after a majority of Izumo had been pacified, sea-faring pirates from Tango province (including Nasa Nihonnosuke) departed so, having been left behind, he became disheartened and started the rebellion.

There is also research that takes a completely different view of events.  Namely, Tamekiyo was, from the beginning, allied with the Mōri and, after defeating the pirates from Tango in Oki Province, he crossed to Mihonoseki and attacked.  Rather than Tamekiyo, his younger brother, Kiyozane, who assisted the Amago revival army in their landing in Izumo and provided support at the Battle of Harate.

Strategy of Yamanaka Yukimori

The Amago revival army made plans to cross the seas and launch a surprise attack against Oki Tamekiyo, but could only secure a small number of vessels so fought with a small army.  On the vessel on which Yamanaka Yukimori sailed to Mihonoseki, he strictly ordered his soldiers to abide by the following:

Do not think about a small victory, but commit yourself only to distinguished service.

Do not engage in unnecessary fighting.

Report the outcome of your efforts and those of others without bias.

Abide by my (Yukimori’s) orders in regard to advancing and retreating.

Do not take the heads of rank-and-file soldiers, only those of unit leaders.