Battle of Yuminohama

弓浜合戦

Amago Clan

Izumo Province

Yuminohama

Mōri Clan

Date:  Eiroku 7 (1564)

Location:  Yuminohama in Mihonoseki in Izumo Province

Synopsis:  In the latter part of 1562, Mōri Motonari marched his army into Izumo Province to launch attacks against the main base of the Amago clan at Gassantoda Castle which relied upon Odaka Castle for the supply of provisions.  In 1564, after the Amago army made preparations in Mihonoseki to attack Odaka Castle, Sugihara Morishige, the lord of Odaka Castle, led an army to subdue the Amago, but the Amago won the main battle and then pursued the Mōri to Yuminohama for a secondary clash.  Details vary but the end result was further retreat by the Mōri to Odaka Castle.

Lord:  Amago Yoshihisa

Commanders:  Moriwaki Hisanori, Honda Ieyoshi, Yamanaka Yukimori, Tachihara Hisatsuna, Akiage Munenobu

Forces:  4,300

Losses:  Unknown

Lord:  Mōri Motonari

Commanders:  Sugihara Morishige

Forces:  1,500 to 2,000

Losses:  Unknown

The Battle of Yuminohama occurred in Eiroku 7 (1564) in Yuminohama in Mihonoseki in Izumo Province.  The conflict was waged between the Mōri and Amago armies.

Prelude

During the first half of the sixteenth century, the Ōuchi and Amago clans engaged in conflict across the Chūgoku Region.  In the eighth month of Tenbun 20 (1551), however, Sue Takafusa (later known as Harukata), a senior retainer of the Ōuchi, launched a coup d’état against his lord, Ōuchi Yoshitaka, resulting the death of Yoshitaka in an event known as the Tainei Temple Incident.  This event led to significant change among the distribution of power in the Chūgoku Region.

The Mōri clan, the sengoku daimyō of Aki Province, took advantage of these developments to extend their influence in the region.  On 10/1 of Tenbun 24 (1555), Mōri Motonari, the twelfth head of the clan, defeated Sue Harukata at the Battle of Itsukushima.  In the fourth month of 1557, he eliminated the Ōuchi clan and took over control of Suō and Nagato provinces in an event known as the Subjugation of Bōchō.  In 1559, he sent troops into Bitchū Province, subduing the Shō clan, kokujin, or provincial landowners, aligned with the Amago.  After forming an alliance with the Mimura clan, powerful kokujin in Bitchū, the Mōri succeeded in pacifying the entire province.  In the sixth month of 1562, the Mōri army attacked the base of the Amago in Iwami at Yamabuki Castle and seized control of the Iwami-Ginzan silver mine, garnering control of the province.

Meanwhile, in the wake of the Tainei Temple Incident, the Amago clan expanded their influence into Iwami.  In the Collapse at Oshibara, which occurred either in Kōji 2 (1556) or Eiroku 1 (1558) at Oshibara, the Mōri clan suffered a major defeat by the Amago clan.  The Amago sought to control the silver mine and, in so doing, expand their economic power.  On 12/24 of Eiroku 3 (1561), however, the head of the clan, Amago Haruhisa, suddenly died.  He was succeeded by his eldest son, Amago Yoshihisa.  Owing to a series of missteps in diplomatic policies,  the Amago witnessed a decline in their power.  By the middle of 1562, less than two years after Yoshihisa succeeded his father, the territory governed by the Amago had been reduced only to Izumo and Oki provinces along with the western portion of Hōki Province.

On 7/3 of Eiroku 5 (1562), Mōri Motonari led a march into Izumo with the intention of extinguishing the Amago clan.  After entering Izumo, the Mōri army forced the surrender of a series of influential kokujin aligned with the Amago.  In the twelfth month of 1563, the Mōri established an operational base at Arawai on the Shimane Peninsula and commenced an assault against the main base of the Amago clan at Gassantoda Castle.

Motonari initially adopted a strategy to sever the supply lines to the castle.  On 8/13 of Eiroku 6 (1563), the Mōri army commenced an assault against Shiraga Castle, designated as the first of ten outlying castles known as the Amago Jikki, or the Ten Banners of the Amago, which formed a line of defense to protect Gassantoda Castle.  The castle was captured around the middle of the tenth month in an event known as the Siege of Shiraga Castle.  Shiraga Castle stood on the northern short of Lake Shinji, a strategic location linking the Shimane Peninsula facing the Sea of Japan and Gassantoda Castle.  The fall of this castle severed the supply route for the Amago army between the Sea of Japan and the peninsula.

To the east of Gassantoda Castle, the Mōri army proceeded to attack the western portion of Hōki Province.  Motonari himself noted in a letter that it was critical to secretly arrange for military operations to the west (on the Shimane Peninsula) and the east (western Hōki) of Gassantoda Castle, highlighting the importance of these areas to an assault against the castle.

In western Hōki, the Mōri army regarded Odaka Castle as one of the key sites.  Odaka Castle was situated in the northern portion of western Hōki in a strategic location for travel between Izumo and Hōki provinces.  As a result, this became an important base for supplying provisions from western Hōki to Gassantoda Castle.

While Odaka Castle was regarded as a valued base by the Mōri army, likewise, the Amago army also understood its importance.  Yukimatsu Masamori served as the lord of Odaka Castle.  In the latter part of the fifteenth century, the Yukimatsu clan served Yamana Hisayuki, the military governor of Hōki Province. During the Eishō era (1504 to 1521), the Amago encroached on Hōki while Amago Tsunehisa backed Yamana Sumiyuki (a cousin of Hisayuki).  After Sumiyuki prevailed in conflict against Hisayuki and became the governor,  the Yukimatsu were ousted, but around the summer of 1562, recovered the castle with the backing of the Mōri.

From the fifth to seventh months of 1563, the Amago army launched a fierce assault against Odaka Castle.  At one point during this conflict, owing to the momentum on the side of the Amago, Motonari had resigned himself to the fall of the castle.  Nevertheless, valiant fighting somehow enabled the Mōri forces to hold the castle and the Amago were unable to achieve their objectives.

In 1564, to enable another assault against Odaka Castle and to secure their supply routes to Gassantoda Castle, the Amago forces advanced toward Mihonoseki located on the western tip of the Shimane Peninsula.  After invading Mihonoseki, the Amago army wiped-out the Mōri forces based there, stationed their own troops in place of the Mōri, and proceeded to prepare for another attack against Odaka Castle.

At this time, Odaka Castle was defended by a general in the Mōri army named Sugihara Morishige.  Toward the end of 1563, Yukimatsu Masamori, the lord of Odaka Castle, died of illness.  Morishige then became the lord of the castle and successor to Masamori as the head of the Yukimatsu family.  Upon learning of the developments in Mihonoseki, Morishige led a contingent from Odaka Castle on a march to subdue the Amago forces.  As these movements became known to the Amago, the Amago deployed from Mihonoseki to intercept the approaching Mōri forces and the two sides clashed at Mihonoseki.

Course of events

In this battle, the Amago army achieved victory by successfully intercepting the Mōri forces and then the Mōri withdrew to their base at Odaka Castle.  The details of the battle, however, differ by historical account.

Account according to the military chronicle known as the Unyōgun-Jikki

In this battle, the Amago army separated into two divisions while the Mōri army remained as a single force.  The conflict began with a clan between the First Division of the Amago army led by Moriwaki Hisanori and Honda Ieyoshi on one side and a division of 2,000 troops led by a general in the Mōri army, Sugihara Morishige, on the other side.

During this initial clash, the Mōri skillfully took advantage of the natural terrain forming a bottleneck to defeat the Amago.  After the First Division in the Amago army retreated in defeat, the second division of 1,000 soldiers led by Yamanaka Yukimori and Tachihara Hisatsuna (who initially held back) joined the battle.  The Second Division of the Amago positioned mounted soldiers on all four sides and concentrated their attack with arquebusiers and archers to challenge the Mōri army.

In this second clash, the Amago army overwhelmed the Mōri.  Unable to maintain their positions, the Mōri soldiers began to flee in defeat.  After retreating a distance of approximately ten kilometers, the Second Division of the Amago led by Akiage Munenobu who had been held back as the rear guard disrupted the Mōri formations which collapsed, causing the Mōri to flee in the midst of chaos on the battlefield.

The routed forces from the Mōri army fled to Yuminohama and attempted to re-group.  Sugihara Morishige, a bushō in the Mōri army, planted a battle flag on a small hill and gather between 600 and 700 troops.  At this time, however, Yoshida Hachirōzaemon, a general in the Amago army, led a detached unit on an ambush that resulted in further pursuit of the Mōri forces who incurred losses in their retreat to Odaka Castle.

Account according to the military chronicle known as the Intoku-Taiheiki

In preparation for the battle, the Amago army separated into two divisions, whereupon the Mōri army followed suit by creating two divisions to establish their formations.  The original plan of the Amago army was for the First Division to pull-back in an apparent defeat, thereby enticing the Mōri to chase after them.   This, it was planned, would disrupt the formations of the Mōri army, permitting the Second Division of the Amago army an opportunity to attack and rout the enemy forces.

The battle began with a clash between the First Division of the Amago army comprised of 1,000 soldiers led by Moriwaki Hisanori and Honda Ieyoshi on one side and the First Division of the Mōri army with 500 soldiers led by Irie Ōkura-shōyū and Irie Saemon-no-jō – bushō in the Mōri army.

After the outbreak of hostilities, the First Division of the Amago army followed their original plan to pull-back in apparent defeat to entice the Mōri to give chase with the aim of causing a breakdown in the Mōri formations.  Contrary to the expectations of the Amago, however, the Mōri army reinforced their positions and did not move, preserving their formations and foregoing a pursuit of the Amago forces.

The Second Division of 2,000 soldiers led by Yamanaka Yukimori and Ushio Danjō-no-chū initially held back.  After changes to the battle plans, the second division replaced the First Division and clashed with the Mōri but was overwhelmed by a hail of arrows.  In a bid to recover their momentum, the First and Second divisions attempted to re-group and were combined.

At this time, a unit of 300 soldiers led by Yoshida Hachirōzaemon, a general in the Amago army, arrived late to the battlefield but was able to disrupt the Mōri army, allowing Yamanaka Yukimori and Tachihara Hisatsuna an opportunity to re-group.  Meanwhile, Akiage Munenobu, who was held back at the rear of the Second Division, led a battalion of 1,000 soldiers and went around behind the Mōri in an effort to sever the enemy’s route of retreat.  Once susceptible to a pincer attack, the Mōri soldiers stampeded in disarray.

In the midst of being routed, a commander in the Mōri army named Sugihara Morishige retreated with 50 mounted soldiers a distance of seven to eight kilometers while under pursuit by the Amago army.  After arriving in Yuminohama, he planted a battle flag on a sand hill on the beach and re-grouped with a contingent of 500 soldiers who had fled the battle.  Once the Amago forces arrived, the Mōri repelled them by firing their arquebuses and shooting arrows at them.  After chasing the Amago for approximately 500 meters, the Mōri returned to their position and assembled 1,500 troops, dividing them into two divisions to set-up an encampment.

Next, the Amago army organized a contingent of 3,000 soldiers and pressed toward the Mōri, but, after seeing the formations of the Mōri army, pulled back so the Mōri did not chase after the retreating forces during a withdrawal to Odaka Castle.

Consequences

After prevailing in the battle, the Amago army attacked Odaka Castle again but could not capture it and were defeated.  Thereafter, the Mōri army continued to govern Hōki Province.  Around the beginning of 1565, the Mōri army controlled all of Hōki, rendering the main base of the Amago at Gassantoda Castle completely isolated.  In the fourth month of Eiroku 8 (1565), the Mōri army commenced an assault against Gassantoda Castle in an event known as the Second Siege of Gassantoda Castle.