Battle of Itsukushima
Date: 10/1 of Tenbun 24 (1555)
Location: Itsukushima in the Seto Inland Sea (Aki Province)
Synopsis: After having usurped Ōuchi Yoshitaka and forcibly taken over the Ōuchi clan, Sue Harukata boldly challenged the Mōri army to a battle on the sacred island known as Itsukushima. In one of the most consequential battles for Mōri Motonari, featuring clashes on land and at sea, the Mōri army, backed by the Kobayakawa forces and the Murakami navy, routed Harukata and his army in the course of a single day. This victory created the conditions for Motonari to launch a campaign known as the Subjugation of Bōchō (Suō and Nagato), becoming the dominant lord in the western provinces of Japan.
Battle of Itsukushima
The Battle of Itsukushima occurred on 10/1 of Tenbun 24 (1555) at Itsukushima in Aki Province. The conflict was waged between the forces of Mōri Motonari and Sue Harukata. Itsukushima is commonly known as Miyajima, or the “shrine island” given the sacred status of the entire island in the history of the Shintō religion in Japan.
In 1551, in the Tainei Temple Incident, Sue Takafusa killed Ōuchi Yoshitaka and seized authority over the Ōuchi clan. He then changed his name to Sue Harukata. The Ōuchi clan based in Suō and Nagato provinces had under their command kokujin, or provincial landowners, in Iwami and Aki provinces. Yoshimi Masayori of Sanbonmatsu Castle in Iwami Province raised arms under the banner of ousting the Sue clan. This led, in the third month of 1554, to the Siege of Sanbonmatsu Castle. Ōuchi and Sue forces surrounded Sanbonmatsu Castle and called upon Mōri Motonari of Aki to join the siege but, in the fifth month, Motonari severed ties with the Ōuchi and Sue and captured four castles including Sakurao Castle. The Mōri army also occupied Itsukushima. The break in relations between the Mōri on one side and the Ōuchi and Sue on the other is known as the Separation of Suō and Aki. To prepare for a final showdown against the Sue, Motonari bolstered his naval forces and strengthened his defenses on Itsukushima and at castles in the environs of Hiroshima Bay.
Based on Aki Province, on 5/15, the Mōri invaded the Kuga District of Suō, clashing with Sue forces at Oze and Mishō. In response to the revolt from Motonari, Sue Harukata urgently dispatched a retainer named Miyagawa Fusanaga. On 6/5, the Miyagawa forces were defeated at the Battle of Oshikibata. After this battle, the Mōri army advanced into an area called Yamazato in the Saeki District of Aki but encountered resistance in an uprising by lower-level officials of the Imperial Court aligned with the Sue. In the eighth month, Mōri Takamoto deployed and, while persisting to attack, surrounded a portion of the ikki forces and, on 10/25, toppled the stronghold of Tomoda Takamori. It is surmised that Motonari sought to capture Yamazato as a means to invade Suō and pressure the Ōuchi and Sue army from the rear after the Ōuchi and Sue laid siege to Sanbonmatsu Castle. The difficulties encountered in seizing Yamazato may also have had an impact on the strategy of the Mōri army.
The battle between the Mōri and Sue extended to the seas. In the middle of the sixth month, the Mōri navy attacked Tomidaura (an inlet) near Wakayama Castle. In response, the Sue navy launched a separate attack against Itsukushima but the defenses at Miyao Castle thwarted an attempted landing by the Sue forces. In the seventh month, the Sue persuaded security forces from the Mōri navy based at Kure and Nōmi to defect to their side, but, in the ninth month, other security forces from the Mōri and Kobayakawa destroyed them and occupied Nōmishima.
During the Siege of Sanbonmatsu Castle, the Ōuchi and Sue army could not move their main division so the situation did not escalate into a large-scale battle against the Mōri army, but at the end of the eighth month (or on 9/2), after a settlement was reached with Yoshimi Masayori, Harukata turned his attention toward countering the Mōri.
Planning and strategy
Immediately after the Battle of Oshikibata, in a letter dated 6/7 of Tenbun 23 (1554) from Sue Harukata to Masuda Fujikane (a kokjuin in Iwami), Harukata considered the possibility of joining forces with the Amago clan of Izumo Province to launch a pincer attack against the Mōri. On 11/1, an event occurred by which an elite military corps known as the shingutō were purged from the Amago clan so, owing to this internal conflict, Harukata was not able to ally with them. Meanwhile, Mōri Motonari sought to contain the Amago by supporting the Mimura clan of Bitchū Province and the Fukuya clan of Iwami Province who were opposed to the Amago clan.
On 9/10, Motonari sent a secret letter to Shōni Fuyuhisa of Hizen Province urging him to raise arms. The Shōni clan were attacked by the Ōuchi and lost their territory in northern Kyūshū (Buzen and Chikuzen provinces) so aimed to counter the Ōuchi and Sue clans.
Around 1554, the Mōri entered into a marital relationship with Murakami Michiyasu (of the Kurushima-Murakami clan) who was a member of the Murakami navy. The eldest daughter of Shishido Takaie, a member of a cadet family of the Mōri, was adopted by Kobayakawa Takakage and wed to Michiyasu. This alignment with the Murakami was a significant boost for the Mōri.
In an effort to ally with a senior retainer of the Sue named Era Fusahide, Motonari reached out to him covertly and, in the second month of 1555, agreed to defect. Nevertheless, he expressed dissatisfaction with the stipend of 300 kan in return for siding with the Mōri and requested an increase whereupon Motonari felt uneasy about Fusahide’s attitude after defecting to the Mōri. Fusahide was well-aware of the power wielded by Motonari so he advocated to the Sue to settle with the Mōri. Although Fusahide had not betrayed Motonari, Motonari had a letter fabricated under the name of Fusahide to show an intent to collude with the Mōri, and then had the Sue get a hold of the letter to believe that Fusahide had betrayed them. As a result, upon orders of Harukata, on 3/16, Fusahide was slayed at the Kohaku Temple in Iwakuni. It can be confirmed from historical materials that Mōri Takamoto (Motonari’s lineal heir) was angered by the demands from Fusahide for an increase to his stipend so the act of collusion is deemed a fact but it cannot be confirmed (as portrayed in military chronicles) that Fusahide was indeed assassinated through the deception of Motonari.
One of the stories associated with the Battle of Itsukushima as described in military chronicles concerns acts by Katsura Motozumi (the lord of Sakurao Castle) to pretend to collude with the Sue. During the succession of Motonari to the headship of the clan, after Aiō Mototsuna (Motozumi’s younger brother of a different mother) and his supporters (including Motozumi’s grandfather, Saka Hiroaki) were purged, Motozumi’s father, Katsura Hirozumi, took his own life. Thereafter, Motozumi made another attempt to fight against Motonari. On the pretext that Motozumi resented Motonari, Motozumi sent a secret letter offering to collude with the Sue along with a written pledge of allegiance. As a means to deceive the Sue and entice them to Itsukushima, Motonari had Motozumi propose to the Sue that if the Sue army attacks Itsukushima, the main division of the Mōri army will take action to defend the island so Motozumi’s unit will then attack the main base of the Mōri at Yoshida-Kōriyama Castle. This story, however, cannot be substantiated from primary sources. Moreover, to convince Harukata, Motozumi, who wrote a seven-page-long pledge, remained in Sakurao Castle and did not deploy to Itsukushima. Motozumi’s sons participated in form only to fulfill their duties.
Through the solicitations of Motonari, a bushō on the side of the Sue named Kuba Katashige defected to the Mōri. In the opposite direction, Shirai Katatane persuaded Noma Takazane (a kokujin in Aki and the lord of Yano Castle) to abandon the Mōri in favor of the Sue but, prior to the Battle of Itsukushima, he was killed by the Mōri army.
Course of events
In the first month of 1555, after the Separation of Suō and Aki, an attack by the Mōri army ousted Shirai Katatane from Nihojima Castle whereupon he holed-up in Fuchū-Dehari Castle in Aki. Katatane then led naval forces to attack Kusatsu Castle and the base of the Kawachi guard forces of the Mōri, clashing with the Mōri army.
On 3/15, Era Fusahisa commanded a fleet of 140 guard vessels to assault Itsukushima. The next day, after returning to base in Iwakuni, Fusahide was murdered. Thereafter, Noma Takazane abandoned the Mōri and, together with Shirai Katatane, attacked Kaitaura (held by Asonuma Hirohide on the side of the Mōri) and Nihojima Castle.
On 4/8, the groups from the shrine lands of Ogata and Ōtake (in a subordinate relationship with Era Fusahide) attacked Itsukushima with 70 to 80 vessels triggering a small-scale battle.
On 4/9, Motonari led an army of 3,500 men in an all-out attack against Noma Takazane. A total of 1,200 Noma forces and 300 reinforcements from the Sue resisted the attack from their base at Yano Castle but owing to the fall of an auxiliary castle, surrendered on 4/11. Takazane proposed surrender via his father-in-law, Kumagai Nobunao. Although Motonari initially consented, after the defenders came out of the castle, the Mōri demolished them. At this same time, Motonari attacked the Tagaya clan on the islands of Kamagari and Kurahashi.
On 5/13, the Sue navy attacked Itsukushima Castle with 100 vessels and clashed with the Mōri army at Arinoura near Miyao Castle defended by Nakamura Jirōzaemon.
In the sixth month, Motonari himself sailed to Itsukushima to observe Miyao Castle and other sites and assigned 500 soldiers as a castle garrison to Koi Naoyuki and Tsuboi Motomasa.
On 7/7, Shirai Katatane attacked Miyao Castle but was repelled by Koi Naoyuki and the garrison. On 7/10, a navy commanded by Miura Fusakiyo attacked Nihojima Castle with 500 soldiers but owing to resistance by Kagawa Mitsukage and a garrison of 200 men, failed to capture the site. After the defeat, Fusakiyo recommended to Harukata that he land on Itsukushima.
Deployments (9/21 to 9/27)
On 9/21, Sue Harukata led forces from Suō, Nagato, Buzen, and Chikuzen to deploy from Iwakuni. An army of over 20,000 men set sail in a flotilla of 500 vessels from Imazu and Muroki in the Kuga District to head by sea route toward Itsukushima. That evening, the vessels moored in the waters off of the island, and, early in the morning on 9/22, the Sue forces began their landing. With respect to the plans by Harukata to attack Miyao Castle on Itsukushima (in a strategic location for passage by sea), Hironaka Takakane forewarned him of the risk of an attack from the rear by the Mōri army. The Sue army landed at Ōmoto-no-ura, with Miura Fusakiyo and Yamato Okitake serving in the vanguard. The main base for Suekata was located at Tō-no-oka with an unobstructed view of Miyao Castle. Owing to the number of Sue forces, their base extended from the Daishō Temple to a mountain known as Misen. Guard vessels were amassed from Sugi-no-ura to the north to Suyaura to the south. The Sue army began to attack Miyao Castle from the roads along the ridgelines of the mountains and attempted to sever the sources of water to the castle.
On 9/24, after receiving news that the Sue forces had landed on Itsukushima, the Mōri army departed Satō-Kanayama Castle and arrived at Kusatsu Castle which also served as a naval base. The Mōri army commanded by Motonari and Takamoto included the forces under Kikkawa Motoharu in addition to kokujin from Aki including the Kumagai, the Hiraga, the Amano, and the Asonuma clans. The naval forces led by Kobayakawa Takakage also converged. At this time, excluding the members of the garrison at Miyao Castle, the Mōri army was comprised of 4,000 soldiers and 110 to 130 vessels (in the Mōri and Kobayakawa navy). Including the additional forces in the Innoshima-Murakami navy under the command of the Kobayakawa, the total fleet was less than 200 vessels. While Nomi Munekatsu, a senior retainer of the Kobayakawa, engaged in negotiations with the Noshima-Murakami and Kurushima-Murakami for their support, Motonari waited for reinforcements at Kusatsu Castle.
On 9/26, Motonari assigned 50 to 60 vessels to Kumagai Nobunao, dispatching them as reinforcements to Miyao Castle. In a letter dated that same day, Motonari instructed Takakage to urge the Murakami navy to hurry with reinforcements. The feelings of impatience conveyed in the letter may have owed to the threatening situation at Miyao Castle.
On 9/27, by this time, the moats around Miyao Castle had been filled in and the water source severed, but preparations were not complete on 9/28 and 9/29 so plans for an all-out attack were postponed. Meanwhile, Motonari gave instructions to Takakage that he could not wait any longer for those in Kurushima so he should deploy only with the Mōri and Kobayakawa navy to Miyao Castle.
Final preparations (9/28 to 9/30)
On 9/28, Motonari departed Kusatsu Castle and advanced all of his forces to Jigozen. The common view is that, on this day, the Murakami navy rushed forward with 200 to 300 vessels as reinforcements to the Mōri army. This date is noted in several accounts and it is surmised that the Mōri set sail early on 9/29, but under another theory the Mōri arrived in Jigozen on 9/29 and the Murakami came that same day, sailing on 9/30 such that the battle occurred on 10/1. In one account, Motonari instructed the Murakami navy to go around Itsukushima and approach the Sue forces from the west using the sound of their oars and by yelling to pretend that the Murakami were siding with the Sue; however, a letter written by Hironaka Takakane on that same day acknowledges that after seeing that the Murakami navy sided with the Mōri, the Sue were placed at a disadvantage in naval power.
On 9/30, the Mōri and their allies were divided into three armies: The first army (the main division of the Mōri) led by Motonari, Takamoto, and Motoharu; the second army (the Kobayakawa) led by Takakage which converged with the soldiers from Miyao Castle; and the third army comprised of the Murakami navy. The armies then prepared to sail to Itsukushima. In the evening, the weather began to turn fierce with lightning strikes accompanied by strong winds and rain. Motonari, however, said it was a day of good fortune, convincing his men that the stormy weather would serve as protection from heaven and decided to deploy at 6:00 PM. One account notes that, soon thereafter, the storm settled down. To avoid being noticed by the enemy, only Motonari’s vessel had a fire suspended in an iron basket while the flotilla secretly took a roundabout course toward Itsukushima from the east. Around 11:00 PM, the forces landed on the eastern shore of Itsukushima known as Tsutsumigaura. Motonari ordered Kodama Narikata to return all naval vessels and notified the soldiers of his decision to establish a base with their backs to the water so there would be no retreat and they must fight to the end. Thereafter, with the Kikkawa division serving in the vanguard, the forces proceeded on a mountain road toward the Bakuchio ridge.
The second and third armies sailed west under cover of darkness to Ōno-Seto (a strait to the west of Itsukushima) and, after making a big detour, arrived near the large archway to the Itsukushima Shrine. Around 9:00 PM, the Kobayakawa forces arrived at the waters off of the shrine, and upon the counsel of Nomi Munekatsu, took advantage of torrential winds and darkness (which made it difficult to discern friend or foe) to approach the shore. These forces landed under the pretext of being additional forces from Chikuzen seeking an audience with the lord of the Sue (Harukata). The third army (the Murakami navy) waited offshore until the commencement of hostilities.
Main battle (10/1)
At 6:00 AM on 10/1, the Mōri army launched a surprise attack. The Mōri army traversed Bakuchio, and while raising war cries, chased down the Sue forces from behind (from the side of the Momiji Valley). A detached division (the Kobayakawa division) and soldiers from Miyao Castle acted in concert by ascending the main base of the Sue at Tō-no-oka. Observing that battles had ignited on Tō-no-oka, the Murakami navy waiting offshore Itsukushima commenced attacks against the Sue navy, burning their vessels. Caught off guard by storms the night before, and owing to their numbers, the Sue could not easily maneuver on the narrow island. One account noted that the rout was so one-sided that the Sue (including Hironaka Takakane) withdrew toward the western mountains without shooting a single arrow.
In the midst of a pincer attack by the Mōri, the Sue forces scrambled in an effort to flee the island, with vessels sinking and men drowning in a scene of mayhem. Hironaka Takakane, Miura Fusakiyo, and Yamato Okitake led a unit of soldiers to mount a valiant defense, but order could not be restored amidst the chaos and Harukata aimed to escape from the island. Harukata and others fleeing west were pursued by the Kikkawa division. Hironaka Takakane and Hironaka Takasuke (father and son) led 500 men to the south of the Itsukushima Shrine with the Takikō Road at their back, intent on impeding the progress of the pursuing forces. At this time, 300 soldiers from the Aokage, Hatano, and Machino clans in the Sue army pierced the Kikkawa division from the flank, giving a temporary advantage to the forces commanded by Takakane. Reinforcements led by Kumagai Nobunao and Amano Takashige rushed to support the Kikkawa division, forcing Takakane and his men to retreat to the Daishō Temple. Continuing his efforts to halt the pursuit by the Mōri forces, Takakane started a fire. There is a story that Motoharu, fearing the fire would burn down the Itsukushima Shrine, ordered soldiers to battle the blaze. Although Harukata and his forces originally came ashore at Ōmoto-no-ura, there were no vessels left behind by which to flee the island. As the forces under Takakage caught up with the Sue, Fusakiyo served as their rear guard. Fusakiyo and his men mounted a violent resistance, even imposing injuries on Takakage. After dousing the fire, the forces under Motoharu joined Takakage’s men to defeat the Sue and finally kill Harukata. Fighting to the end, Fusakiyo carried responsibility for recommending that the Sue forces cross to Itsukushima.
Accompanied by only a small party of servants, Harukata headed west to Ōeura but there was no boat. According to one account, he crossed the mountains and ventured to Aonori Beach on the eastern shore to search for a boat and then retraced to Takayasu-ga-hara in the mountains but this does not appear possible given the terrain and the timing. At Ōeura, he committed seppuku and, by customary practice, was decapitated in the process by Ikaga Fusaaki (or Ikaga Takamasa). Servants remaining with him to the end included, in addition to Fusaaki, Kakinami Takamasa and Yamazaki Takakata. After hiding Harukata’s head in the mountains, these three attendants martyred themselves.
After fighting against Kagawa Mitsukage, Yamato Okitake was captured. Mitsukage recalled that Motonari previously sought to engage Okitake as a retainer so he captured him alive. As a result, Okitake was sent to Nihojima Castle which, for the time being, had been assigned to Mitsukage. One month later, upon orders of Motonari, Okitake was slain.
With the exception of lingering resistance by a group led by Hironaka Takakage (as described below), the battle came to an end around 2:00 PM.
Aftermath (10/2 to 10/5)
After decimating the main divisions of the Sue army, Motonari ordered his troops to track down remnants of the enemy forces who had fled in defeat across the nearby islands.
Meanwhile, after clashing against Kikkawa Motoharu in the environs of the Daishō Temple, Hironaka Takakane retreated via valleys alongside a sacred mountain known as Misen. Together with a group of 100 to 300 men, he holed-up in a rocky area called Ryūgabanba at Emagatake on an adjacent mountain. After the Kikkawa forces encircled the mountaintop, Takakane and his men resisted their fierce attacks for three days but were then completely decimated.
On 10/5, while searching for Harukata’s head, the Mōri army captured a youth who served as a servant in charge of footwear for Harukata. In exchange for offering to spare his life, they inquired as to the location where Harukata’s head was hidden. After discovering the head, Motonari pulled his forces out of Itsukushima and marched triumphantly to Sakurao Castle on the opposite shore. An inspection of enemy heads was conducted at this castle. During the inspection, Motonari said: “He was a betrayer who killed his lord and committed the most serious crimes under the code” after which he hit the head three times with a shoe and then had it buried at the Tōun Temple.
According to one account, among the forces of the Sue army, a total of 4,780 were killed and over 3,000 captured. The entirety of Itsukushima is regarded as sacred and the site of the Itsukushima Shrine so Motonari had all of those who were killed moved to Ōno on the opposite shore and removed the dirt from areas soaked in blood. Furthermore, he had his men wash with sea water the buildings and corridors of the Itsukushima Shrine that had been stained with blood to purify them. For a period of seven days after the battle, he made dedications to the shrine and held kagura, or ritual dances and ceremonies to mourn the souls of those who died in battle.
Following the loss of Sue Harukata in this battle, the Ōuchi and Sue clans witnessed a rapid decline.
On 10/5, after completing the inspection of heads at Sakurao Castle, Motonari moved the main division of the Mōri army to Ogata and commenced the invasion of Suō and Nagato provinces. This campaign is known as the Subjugation of Bōchō. On 4/3 of Kōji 3 (1557), Ōuchi Yoshinaga (the younger brother of a different mother of Ōtomo Sōrin and nephew of Yoshitaka) formerly backed by Harukata was cornered in Katsuyama Castle and took his own life. This marked the end of the Ōuchi clan as a daimyō family. Thereafter, the Mōri annexed the former territory of the Ōuchi, becoming a major daimyō in western Japan. Aiming for the wealth of Hakata and the Iwami Silver Mine (both of which had been controlled by the Ōuchi), Motonari initiated hostilities against the Ōtomo clan of Bungo Province in northern Kyūshū and the Amago clan in the Sanin region.
Soon after the battle, the Kuwahara and Kutsunoya clans of the Yashirojima security forces comprising the Ōuchi navy affiliated with the Mōri and, after the Ōuchi clan was extinguished, Shirai Katatane, a kokuijn from Aki, surrendered to the Mōri enabling the Mōri navy to expand its power. Once Motonari began to anticipate a conflict with the Sue, starting from around 1551, he set about in earnest to build a navy under his direct control. The Mōri navy that evolved at the time of the Battle of Itsukushima made significant contributions in battles against the Ōtomo and Amago clans as well as later battles against Oda Nobunaga.
The Mōri forces (including the Kikkawa and Kobayakawa divisions in addition to kokujin from Aki Province) totaled from 3,000 to 4,000 men. In addition to the main divisions, there were 500 men in the garrison at Miyao Castle and 800 remaining behind to defend Yoshida-Kōriyama Castle. There is also a theory that, including other elements who participated on the side of the Mōri, the total number of forces mobilized for Itsukushima significantly exceeded 5,000 men.
Naval forces commanded by Motonari included 50 to 60 vessels from the Mōri navy (Kawanouchi security forces) and 60 to 70 vessels from the Kobayakawa navy (Numata security forces).
In military chronicles, Sue Harukata led an army of 20,000 to 30,000 soldiers hailing from Suō, Nagato, Buzen, and Chikuzen provinces and landed on Itsukushima. Other accounts raise questions regarding force levels, noting that other senior retainers from the Ōuchi clan including the Naitō and the Sugi did not participate in the battle and that land-based forces were dispersed so that less than 10,000 members of the Sue army landed on Itsukushima. Moreover, losses incurred by the Sue in this battle totaling 4,700 killed in action and 3,000 captured, suggesting that around 8,000 Sue troops landed on Itsukushima.
The naval power of the Sue army included 500 to 600 vessels based at Yashirojima (the Yashiro forces and Yashiro security forces). However, after Miyao Castle was surrounded by the Sue army, based on the fact that a flotilla of 60 to 70 vessels in the Mōri navy came as reinforcements for the castle and a letter from Hironaka Takakane in which he decried the shortage of naval power, the traditional view that the Sue navy had sufficient resources to block access in the waters off the coast of Miyao Castle.
The Murakami navy sailing approximately 200 to 300 vessels partook in the battle as reinforcements to the Mōri. There are assorted theories concerning the movements of the three families of the Murakami, namely the Innoshima-Murakami, the Noshima-Murakami, and the Kurushima-Murakami, each of which exercised a degree of autonomy in their actions. Under one theory, the Innoshima-Murakami were the only one of the three families to participate in the battle.
There is a view that the Murakami definitely served on behalf of the Mōri because, prior to the battle, they were under the command of the Kobayakawa clan and, from the era of Murakami Naoyoshi (the fifth head of the Innoshima-Murakami), the family was close to the Mōri. It is noted that Murakami Yoshimitsu (the sixth head of the Innoshima-Murakami) dispatched a senior retainer named Suenaga Kagemichi (later known as Isokane Kagemichi) but owing to the absence of references to his participation in the battle in authenticated sources, this cannot be verified. If he did participate, it is believed that the Innoshima-Murakami navy had already joined by the time that the Mōri army amassed at Kusatsu Castle on 9/24.
Regarding support from the Noshima-Murakami clan led by Murakami Takeyoshi, references appear in war chronicles and memorandums compiled during the Edo period, but his name does not appear in authenticated sources. On 5/12 of Tenbun 23 (1554), the Separation of Aki and Suō occurred when Mōri Motonari of Aki Province severed relations with Sue Harukata and Ōuchi Yoshinaga of Suō Province. After this break, there are references to Takeyoshi siding with the Sue, so it is not known whether he participated in the battle. As a band of pirates, the Murakami had a strong tendency to act independently and to be opportunistic when it served their interests so it is surmised that Motonari did not have excessive expectations regarding their level of contribution.
With respect to the arrival of the Murakami navy on 9/28 (or 9/29), Motonari noted in a letter “Our lives depended upon the support from Kurushima.” This is the only one of the three families noted to have participated in the battle.
Force numbers and awards
The traditional view is that the Mōri army waged this battle against a Sue army comprised of over five times as many soldiers. Based on assorted strategies and a surprise attack on Itsukushima, despite their lesser numbers, the Mōri achieved a brilliant victory over the Sue. Under another view, however, the Sue army may have been less than 10,000 men, and rather than enjoying an overwhelming numerical advantage, the Sue may have vied against the Mōri with a significantly smaller force. This theory is based on a letter from Hironaka Takakane addressed to his wife just prior to the onset of the battle in which he noted his last wishes.
During land surveys later conducted in the era of Toyotomi Hideyoshi, the former territory of the Ōuchi clan in Suō, Nagato, and one-half of Iwami Province totaled from 600,000 to 700,000 koku. A territory of this size would permit the mobilization of over 20,000 men. Around the time of the battle, the political situation under Harukata was unstable, and he had to allocate a portion of his forces toward the defense of his territory. Furthermore, some of the retainers and kokujin, or provincial landowners, in his territory did not obey the mobilization orders. Therefore, is more than likely that Harukata could only mobilize less than 20,000 men.
After the Battle of Itsukushima, the letter of commendation that Motonari would ordinarily have issued to his retainers have not been located. The absence of these letters has raised issues as to whether Motonari commanded the battle. According to one theory, the battle of Itsukushima was waged between the Murakami navy and the Sue clan so Motonari was not in a position to issue commendations. It is therefore surmised that, in the Edo period, the achievements of the Murakami navy were subsequently attributed to the Mōri family.