The Strategic Context of Japan’s Coastal Fortifications

Following their retreat from northern Korea in 1597, Toyotomi Hideyoshi ordered his forces to construct a network of coastal fortresses—known as wajo—across southern Korea. These castles, built near existing Korean fortifications, aimed to secure supply lines and maintain a foothold for future campaigns. Key commanders like Katō Kiyomasa, Konishi Yukinaga, and Shimazu Yoshihiro were tasked with defending these strongholds while the bulk of Japanese forces withdrew to the homeland.

This decision revealed Japan’s waning momentum in the war. Hideyoshi’s initial ambition to conquer Ming China via Korea had stalled, and the wajo strategy reflected a shift to defensive consolidation. The castles—scattered from Ulsan to Suncheon—became flashpoints for the war’s final phase, drawing Ming and Korean forces into brutal sieges.

The Construction of Ulsan Castle: A Race Against Time

In October 1597, Katō Kiyomasa began constructing Ulsan’s Dosan fortress, a hilltop citadel with concentric defenses (honmaru, ninomaru, sannomaru). Japanese records describe relentless labor:

– Forced Mobilization: Korean civilians and Japanese soldiers worked day and night under brutal conditions. Failure meant beatings or execution.
– Resource Extraction: Forests were stripped bare for timber; those who gathered inadequate materials were forced back into the mountains.
– Human Cost: The monk Keinen’s diary recounts starving laborers, rampant disease, and Japanese slave traders abducting Koreans.

By December, the unfinished castle faced an existential threat: a 42,000-strong Ming army, led by generals Xing Jie and Yang Hao, was advancing toward Ulsan.

The Battle of Ulsan: Tactics and Stalemate

### Phase 1: The Assault on Japanese Outposts (December 23–24, 1597)
Ming cavalry, exploiting poor Japanese scouting, ambushed forward positions at Nongso. General Li Rumai’s feigned retreat lured defenders into a trap, where Mongol horsemen under Ma Gui shattered Japanese ranks. The monk Keinen wrote: “Smoke choked us; flames consumed the castle. Thousands perished—laborers and warriors alike.”

### Phase 2: The Siege of Dosan (December 25–31)
Ming forces surrounded the inner citadel but faced crippling challenges:
– Terrain: The steep, stone-reinforced Dosan rendered artillery ineffective. Japanese matchlocks (teppō) rained fire on attackers.
– Leadership Disputes: Ming officers quarreled over credit. General Chen Yin’s near-breakthrough was halted when Ma Gui—jealous of Li Rumai—ordered a withdrawal.
– Weather: Torrential rain turned camps to quagmires. Ming troops, lacking shelter, suffered frostbite and desertions.

### Phase 3: Japanese Relief and Ming Retreat (January 1–4, 1598)
As starvation gripped Dosan, Katō Kiyomasa nearly committed suicide—until a downpour replenished water supplies. On January 4, 30,000 Japanese reinforcements arrived. Ming forces, exhausted and outflanked, withdrew in disarray. The rearguard, unaware of the retreat, was annihilated at Jeontan.

Legacy and Historical Reckoning

### Casualties and Controversy
– Ming Losses: Official reports cited ~1,600 dead and 2,900 wounded, though critics like Ding Yingtai inflated numbers to 20,000.
– Japanese Losses: ~1,200 confirmed killed, with thousands more perishing from disease and exposure.
– Korean Toll: 298 dead, 876 wounded, and 4,982 desertions—highlighting the Chosŏn army’s fragility.

### Strategic Impact
The siege exposed weaknesses on both sides:
– Japan: The wajo were unsustainable without naval supremacy, foreshadowing Hideyoshi’s failed campaign.
– Ming: Poor coordination and siege tactics contrasted with earlier victories (e.g., Pyongyang). The debacle led to Yang Hao’s dismissal.

### Modern Echoes
Ulsan’s trenches and starved defenders mirror later sieges—from Qing struggles in Jinchuan to WWII’s island warfare. The battle remains a case study in logistical overreach and the limits of premodern siegecraft.

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Note: Measurements like chō (~109 meters) and ken (~1.8 meters) are retained for historical accuracy. Primary sources include The Annals of King Seonjo, Keinen’s Chōsen Nikki, and Ming military reports.