Introduction: Korea’s Overlooked Military Prowess

Among the seven powerful states of the Warring States period, Korea (Han) often ranks as the second least prominent in historical records. Yet this seemingly weak state occupying the central plains possessed some of the finest weapons of its time. The famous saying “All the finest swords under heaven come from Han” reflects Korea’s reputation for producing exceptional iron longswords, numerous examples of which have been excavated from late Warring States period tombs.

The Legendary Arms of Korean Soldiers

Korean infantry were renowned for their superior close-combat weapons and armor. The “Strategies of the Warring States” records: “The swords and halberds of Korean soldiers all come from Mingshan, Tangxi, Moyang, Hebo, Dengshi, Wanfeng, Longyuan, and Da’e. These weapons can sever horses and cattle on land and strike down swans and geese in water, cleaving through any enemy’s defenses.” Korean soldiers were completely equipped with armor, shields, helmets, iron masks, leather armguards, and other protective gear.

However, Korea’s most famous weapons were its crossbows. The same text describes: “Korean soldiers draw their bows and shoot, firing continuously without pause. Their arrows strike the chest at long range and pierce the heart at close quarters.” Another passage states “All the strongest bows and most powerful crossbows under heaven come from Korea,” leading many modern readers to assume the Korean army primarily consisted of crossbowmen.

The Elite “Chae-sa” Infantry

This represents a significant overinterpretation. Following Wei’s establishment of its elite “Wei Martial Corps,” all states developed their own elite standing armies based on this model. Korea was no exception, creating an elite infantry force called the “Chae-sa” (材士, meaning “talented warriors”). Strategists described these troops: “With the courage of Korean soldiers, clad in strong armor, wielding powerful crossbows, and carrying sharp swords, one man is worth a hundred – this goes without saying.”

Later generations often mistakenly believed Korean infantry primarily used swords and crossbows. In reality, while these were Korea’s signature military products and a source of royal pride, it would be overly simplistic to assume Korean infantry only employed these two weapons. Even the renowned Wei Martial Corps were said to be capable of drawing “twelve-stone crossbows,” yet no records suggest they primarily fought with ranged weapons.

The term “Chae-sa” originally referred to soldiers of exceptional strength and bravery, regardless of their weaponry. By the Qin and Han dynasties, local infantry were often called “Chae-gwan” (材官), meaning locally selected men of outstanding physical ability. The Han dynasty divided local forces into “cavalry” and “infantry” (材官), clearly using “Chae-gwan” as the term for foot soldiers.

Korea’s Military Industry and Technology

Evidence suggests Korea maintained an elite infantry force renowned for its heavy armor protection. These soldiers were specially selected for their exceptional physical abilities and equipped with Korea’s finest weapons – powerful crossbows and iron longswords. In battle, Korean Chae-sa infantry primarily used the era’s most common polearms like spears and halberds. Their reputation for crossbows likely stemmed from fielding them in greater proportions than other states.

The crossbow represented the most technologically sophisticated weapon of the pre-Qin era. Its ingenious trigger mechanism was a closely guarded secret that gave the Central Plains peoples an advantage against traditional steppe enemies. While archery required years of strength training and practice (taking over a year to train a competent military archer), a complete novice could become an effective crossbowman in just three months.

The Crossbow’s Revolutionary Impact

Crossbows fundamentally changed warfare by separating the loading process from aiming and release, allowing soldiers to utilize much more powerful bows. Pre-Qin and Han dynasty crossbows differed significantly from their Tang-Song counterparts – while later crossbows specialized in penetrating heavy armor, earlier versions essentially functioned as mounted powerful bows designed for maximum draw weight and range.

Warring States period crossbow triggers represented a stroke of genius – a simple pull on the “hanging knife” (trigger) would immediately release the “teeth” holding the string, unleashing the bow’s stored energy. The trigger mechanism was an efficient, interconnected mechanical device with five main components: the teeth, rear sight, trigger, locking piece, and pin. By the Han dynasty, an enclosing “frame” was added to secure all components within a recess in the stock.

Korea’s Iron Industry and Weapons Production

Korea’s advanced iron industry supported its military might. Archaeological evidence from sites like Tai’e (in modern Xiping County, Henan) reveals Korea mastered liquid iron smelting early. This required solving two major technical challenges: building sufficiently large and sturdy furnaces for proper heat conduction and redox reactions, and developing adequate bellows to maintain the necessary 1150-1300°C temperatures.

Compared to the European experience (where bloomery iron appeared in the 9th century BCE but liquid iron smelting only emerged in 14th century Germany), China’s rapid progress in iron technology was remarkable. This advancement built upon China’s sophisticated bronze metallurgy – Western Zhou copper smelting furnaces up to 1.7 meters tall with multiple air inlets and specialized bellows equipment from the Spring and Autumn period provided crucial technological foundations.

The Paradox of Korean Military Performance

Despite their superior equipment, Korean armies often underperformed in offensive campaigns. The strategist Wu Qi critiqued: “The people are exhausted by war yet accustomed to arms. They think little of their commanders and scorn their meager pay. Soldiers lack the will to die, so though trained, they cannot be effectively used.”

Frequent warfare bred resentment among soldiers, while commanders lacked prestige. Compared to Central Plains living costs, military pay proved inadequate, resulting in generally low morale. Well-equipped and skilled though they were, Korean forces showed little initiative in territorial expansion – since soldiers gained little from new conquests that mostly benefited nobles.

It took five Korean rulers 49 years to conquer the state of Zheng, with Zheng often holding the upper hand. During the Five-State Alliance against Qi, Korean forces achieved little. At Huayang, a Korean relief force was crushed by the long-marching Qin army. At Yique, Korean troops “presented” the Qin with nearly 200,000 heads as battle trophies.

Yet in defensive battles, Korean armies displayed astonishing resilience. During the Maling campaign, though besieged by the formidable Wei Martial Corps, Korean forces held out until news of Wei crown prince Shen’s defeat forced a settlement. At Yiyang, Korean defenders held the isolated city for months, inflicting heavy casualties that indirectly caused Qin general Gan Mao’s downfall. Though weak, Korea stubbornly defended the Jin region for decades. As the state directly blocking Qin’s eastern expansion, Korea lasted until the very end – a testament to its defensive capabilities.

Legacy of the Chae-sa

Korea’s elite infantry represented a fascinating case of military specialization during the Warring States period. Their combination of advanced metallurgy, innovative weapons technology, and selective recruitment created a formidable defensive force, even if their offensive capabilities proved limited. The Chae-sa’s legacy lies in demonstrating how even smaller states could develop distinctive military advantages through technological and organizational innovation during this era of intense competition.

Their story also highlights the complex relationship between equipment, training, and morale in military effectiveness – even the best weapons cannot compensate for systemic weaknesses in motivation and leadership. Korea’s experience would be repeated by later states facing the rising Qin juggernaut, making the Chae-sa both a unique phenomenon and a cautionary tale of the Warring States period.