Infantry formations of the Imjin War — Part 2

Zhejiang infantry unit rotation

『迭相進退, 左旋右抽, 各臻其妙。』

"Then (they) arrayed in intervals (and) advanced and retreated by turn, spun left and drawn right, each had its own ingeniousness."

From Korean description, it is evident that Imjin War-era Zhejiang troops still practiced some forms of unit rotation, allowing fresh troops to rotate in to relieve exhausted troops in combat. Not only this greatly improved overall resiliency and staying power of the formation, it also allowed for disciplined and controlled withdrawal in case the battle went south. It should be noted that unit rotation required considerable level of training and discipline, indicating that the training regime passed down by Qi Ji Guang (戚繼光) remained observed long after his passing.

While details about unit rotation were not discussed in the Korean account, it's likely that the tried-and-true Chou (抽) and Die (疊) methods were still used by Zhejiang infantry.

Japanese disengagement tactic

In many cases, one devastating charge from fierce Japanese warriors was all that it takes to break the morale of enemy troops and trigger a panicked rout. However, should their opponents stand their ground, Japanese troops would quickly find themselves disadvantaged in close combat against an equivalent-sized Zhejiang formation due to the lack of defensive equipment, as well as having significantly worse staying power as they did not use unit rotation. On such occasions, Japanese troops would have to disengage or risk being ground down in prolonged engagement. The second part of Yeo Yeo-moon's explanation wonderfully describes how this was conducted.

Japanese disengagement played out much like the famous Tsuri no Buse (釣り野伏せ) ambush tactic on a smaller scale. Essentially, the entire formation would disperse and meld into the surroundings, leaving behind a token force as bait. If the enemy took the bait and chased after the token force, Japanese troops that went into hiding previously would spring the ambush and attack the enemy from the flanks and rear. This tactic required literal nerves of steel and instinctive grasp of the opportunity to hide as well as to attack to pull off, as the ambush was conducted on an ad hoc basis, and dispersed Japanese troops had to hide individually, with no way of communicating with each other. However, the ability of Japanese warriors to set up organic ambush on the fly without any prior planning and communication was well-known even during the Wokou era.

EXTRA: Suggested Joseon infantry formation

『亟募蹻健少年，胡纓短後者，如吾南軍，赤鞈、白巾, 如吾蜀兵，牛革甲身，束如犀。 造麻牌二萬扇、長標丈八者二萬、鳥槍二萬枝；善射四萬人、刀者二萬人，牌子前品字形，後藏八人：次二槍ㆍ次二標ㆍ次二弓矢ㆍ次二刀。 蓋標一夾以二弓，《兵法》曰：”長槍之後, 繼以弓弩” 此之謂也。』

(You should) urgently recruit able-bodied young warriors, like our Southern troops, (wearing) red armours (and) white headscarves, and like our Shu (i.e. Sichuan) troops, (wearing) cowhide armours tied (to the body) strongly. Make twenty thousand hemp shields, twenty thousand javelins of 5.76 m/18.9 ft length, twenty thousand arquebuses, (recruit) twenty thousand skilled shooters, (and) twenty thousand swordsmen. (For the formation), shieldmen stand at the front in triangle formation, eight men hide behind (them): next is two guns (i.e. arquebusiers), next is two javelins (i.e. pikemen),  next is two bows and arrows (i.e. archers), next is two swords (i.e. swordsmen). Why not let one javelin to be in between two bows, the Art of War says "bows and crossbows follow behind long spears", this is what it means.

— Liu Huang Chang (劉黃裳) suggesting a battle formation to the Koreans.

(Conjectured battle formation with eleven troops.)

(Alternate interpretation of the battle formation with two extra archers.)

Abysmal performance of Joseon army during Imjin War had led to no shortage of complaints and criticisms, and both Chinese and Koreans were keen on introducing new tactics to improve the combat readiness of Joseon army. In a letter written by Liu Huang Chang (劉黃裳), who participated in Imjin War as Zan Hua (贊畫) or chief military staff/advisor of Song Ying Chang (宋應昌), suggested to the Koreans a new battle formation, which will be elaborated below.

It should be noted that Liu Huang Chang's description of the battle formation was vague and imprecise (for example, the numbers simply don't add up, and it's unknown whether the shieldmen were given a weapon, or swordsmen were given a shield or not), although it still gives a basic picture of how the formation functions. The battle formation largely followed the format established by Mandarin Duck Formation, i.e. two identical 5-man teams forming a squad, although it placed much greater emphasis on ranged engagement, with 4 out of 11 troops being dedicated ranged combatants (possibly taking into consideration that the Koreans were great archers), as well as 3 hemp shields at the front to better withstand return fire.

The Koreans ultimately did not follow his suggestion and instead opted for copying Qi Ji Guang's later formation wholesale. Regrettably, Joseon military incompetence was largely a structural and systemic issue and couldn't simply be fixed by adopting new formations and tactics.