“Attack the enemy where they are unprepared; launch an assault when they least expect it”. This famous military sentence is not only a high summary of the Twelve Deceptive Stratagems in The Art of War, but also one of the most critical tactical cores of the entire military classic.
Cao Cao, the top military strategist and warlord of the Three Kingdoms period, made an authoritative annotation on this maxim:
Strike the enemy when they slack off; raid their positions where defenses are empty.
In short, never fight a well-defended enemy head-on. Instead, seize gaps in their defense, take advantage of their mental blind spots, and launch surprise strikes to win victory at the lowest cost. Almost all later military commentators followed this accurate interpretation.
Among countless ancient classic battles that perfectly practice this strategy, Deng Ai’s secret march through Yinping recorded in Records of the Three Kingdoms stands as the most shocking and representative case. This risky one-man gamble completely broke the deadlock of the Wei-Shu war, destroyed Shu Han in one sudden strike, and rewrote the pattern of the Three Kingdoms.
Battle Deadlock: The Impenetrable Jiange Pass
In 263 AD, the Wei court launched a full-scale punitive campaign against Shu Han. Two leading Wei generals took charge of the whole army: Zhong Hui commanded the main force to march straight to Jiange Pass, while Deng Ai led a flank army to coordinate the attack.
Jiange Pass was known as the No.1 natural barrier of Shu Han. The renowned Shu general Jiang Wei stationed elite troops here. Relying on steep mountains and narrow passes, Jiang Wei firmly blocked Zhong Hui’s massive main army. Zhong Hui launched countless fierce assaults, yet failed to make any breakthrough. The whole northern expedition fell into a painful stalemate. The Wei army suffered heavy consumption of supplies and morale, and Zhong Hui even planned to withdraw all troops and abandon the whole invasion mission.
Deng Ai’s Bold Secret Plan: March Through the Forbidden Wilderness
Seeing the battlefield deadlock, Deng Ai submitted a formal military memorial to the Wei court and put forward an extremely bold surprise attack plan, which was fully documented in Biography of Deng Ai · Records of the Three Kingdoms:
“I request to lead a crack force to set off from Yinping, march along remote and rugged mountain paths, bypass Jiange Pass completely, and march straight into Chengdu from the west. My surprise army will strike the core hinterland of Shu Han directly. If Jiang Wei turns back to rescue Fucheng after learning the emergency in Chengdu, Zhong Hui’s main army can advance smoothly without resistance. If Jiang Wei refuses to retreat, the defenders in Fucheng will be extremely weak and defenseless. As an ancient military book The Military Record states: Attack the enemy where they are unprepared; launch an assault when they least expect it. Now we target their undefended rear area, and we will definitely conquer Shu Han.”
Different from ordinary generals who stuck to frontal combat rules, Deng Ai saw the biggest defensive blind spot of Shu Han: Jiang Wei concentrated nearly all elite soldiers on Jiange Pass, firmly guarding the only regular passage into Sichuan, but completely ignored the wild, uninhabited mountain roads in Yinping. In Jiang Wei’s judgment, the 700-li steep mountain wilderness was an impassable natural moat, so no large army could cross here. This universal military consensus became the biggest fatal flaw of Shu Han’s defense system.
A Life-or-Death March: The Most Grueling Raid in Chinese Military History
Deng Ai’s surprise attack was not a simple detour, but a desperate death march against nature. Records of the Three Kingdoms faithfully recorded the extreme hardship of this troop movement in detail:
In the tenth lunar month of winter, Deng Ai led his army across 700 li of uninhabited wilderness starting from Yinping. Soldiers chiseled mountains to open roads and built wooden bridges and plank roads along cliffs. The mountains were towering and valleys extremely deep, bringing unprecedented dangers. Meanwhile, military grain supplies were nearly exhausted, putting the whole army in mortal danger. Deng Ai wrapped his own body with felt blankets and rolled down the steep cliff voluntarily. All officers and soldiers climbed cliffs and trees one after another, advancing in a single file along the dangerous mountain path.
It is shocking enough that ordinary soldiers risked their lives crossing cliffs. More admirable and decisive was Deng Ai himself: as the supreme commander of the whole army, he took the lead rolling down the precipitous cliff wrapped in felt. This move proved how dangerous and inaccessible the Yinping trail was. No general would expect a formal national army to take such a suicidal route to launch an invasion.
Why Could Jiang Wei Not Defend Against This Raid?
Many readers may wonder: Jiang Wei was a top strategist who mastered Sun Tzu’s military theories thoroughly, and even Zhuge Liang, the founding strategist of Shu Han, had long warned of this hidden danger. Zhuge Liang once delivered an accurate strategic judgment on Shu Han’s national defense based on terrain geography:
“Yinping holds the key to the entire defense of Shu”.
It means that though the Yinping trail was extremely steep, remote and uninhabitable, it was a fatal passage that bypassed the impenetrable Jiange Pass and led straight to Chengdu, the heartland of Shu Han. Hence, permanent heavy garrisons were indispensable here.
Sadly, this crucial defensive reminder was neglected in the late period of Shu Han. Many years after Zhuge Liang’s death, Jiang Wei focused all defensive forces on Jiange Pass and completely forgot his mentor’s strategic warning. That is why the fatal defensive loophole emerged.
“Attacking the unprepared”, this tactic never works because the enemy general is foolish and ignorant of defense. Instead, it targets the inherent cognitive blind spot of even wise commanders.
Jiang Wei firmly believed that Yinping’s 700-li no-man’s-land was an insurmountable natural barrier. He judged that all Wei troops could only attack via Jiange Pass. He defended the predictable battlefield perfectly, but ignored the completely unpredictable deadly route. Deng Ai won not by stronger troops or better weapons, but by breaking all conventional military thinking and choosing the “impossible route”. This is the ultimate application of striking unexpectedly.
Hidden Historical Fact: This Military Maxim Originates Earlier Than The Art of War
There is a thought-provoking historical detail hidden in this battle: Deng Ai did not quote sentences from The Art of War in his military report. Instead, he cited the ancient military classic The Military Record: Attack the enemy where they are unprepared; launch an assault when they least expect it.
This record reveals a key historical truth: This world-famous tactical principle was not originally created by Sun Tzu. Sun Tzu summarized and inherited this mature military thought from earlier ancient military documents, and included it into the Twelve Deceptive Stratagems in The Art of War, making this wisdom spread worldwide forever.
Conclusion: The True Essence of Surprise Attack Tactics
Deng Ai’s march through Yinping perfectly interprets the essence of surprise warfare. True military advantage never comes from defeating the enemy’s strongest defense head-on, but from breaking conventional thinking, targeting the enemy’s blind areas, and striking when the enemy lets down their guard.
Natural dangers are not the real military moat; fixed inertial thinking is the deadliest defense loophole on the battlefield. For thousands of years, this timeless military wisdom remains applicable to wars, competitions and all confrontational scenarios: always guard against the predictable dangers, but never ignore the unexpected strikes coming from the blind side.
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