Under the leadership of Tran Quoc Tuan and the General Command, Tran Dynasty’s military forces and people were able to gain a complete victory against the 3^rd Mongol Invasion (1288), effectively destroying the enemy’s ambition of conquering Great Viet. This victory was achieved thanks to many factors, including the flexible and creative use of the stratagem “Wait at leisure when the enemy labour”.

In the beginning of the invasion, when Yuan army captured Phu Luong Passage (Lang Son), Emperor Tran Nhan Tong asked Tran Quoc Tuan for his appreciation. The Grand Prince calmly replied: “Now our troops are already familiar with fighting them; on the contrary, they are afraid of this distant expedition, and still remember the failures in Heng and Guan, thus having no gut to fight. In my opinion, we can destroy them”. He also added: “This year, the enemy’s order of battle is easy to defeat”. This statement is not only an assurance of the general to the Emperor, but also a solid and correct evaluation of the balance of power between our force and the enemy’s by a brilliant politician and military strategist.

A diagram describing the war between Great Viet and Yuan Army

In his book entitled “The Art of War”, Military Maneuvers Chapter, Sun Tzu proposed that a good commander must bring the freshness of his troops to fight the exhaustion of the enemy, gather full strength for his army, cause difficulties for the hostile force, demoralize them and then deal a decisive blow to defeat the adversary - it is “wait at leisure when the enemy labour”. As a master of the art of war, and with the experience learnt from the two previous Mongol invasions, Tran Quoc Tuan and his General Command cleverly and creatively applied this stratagem in leading Great Viet’s army and people to the ultimate victory against the 3^rd Mongol Invasion.

First, proactively prepare for the upcoming war and create a strong and advantageous order of battle. Great Viet entered the war with great confidence and quickly seized the initiative, thanks to the people’s patriotism, the solidarity among the royal court and experience gained from the two previous wars. Once learnt that the Yuan was plotting for another invasion, Tran’s royal court immediately made comprehensive preparation for the upcoming conflict. Tran Emperor entrusted Tran Quoc Tuan - Hung Dao Grand Prince with the position of Commander-in-Chief, responsible for supervising war preparation and leading all the people and military forces. In July 1286, the Emperor order princes and other nobles to recruit more troops, intensify training, manufacture more weapons and build more ships. He also assigned commanders to critical areas, deploying Tran Quoc Toan and Nguyen Khoai to Lang Son, Tran Khanh Du to Van Don, and Tran Nhat Duat to Bach Hac. Later, from October 19 to November 16, 1286, there was a major military exercise conducted to evaluate the nation’s combat readiness.

In addition to the troop and logistical preparation, Tran Quoc Tuan and his command also focused on force disposition. Thanks to his deep understanding about the enemy’s plan and the capability of our force, he decided not to deploy the headquarters and the court’s main contingent near the border and on the enemy’s likely approaches to Thang Long. For better seaborne and inland maneuvers, Tran Quoc Tuan deployed a strong naval force to cover the area from Thien Truong to Thap Son in coordination with land forces positioned between Thang Long and Van Kiep. To slow down and harass the enemy, he drew units from the court’s army to attach to local militias, especially in the key areas. Thanks to this swift and sound preparation together with a comprehensive troop disposition which enabled both strong defensive and offensive operations, the army of Tran Dynasty was able to be present at all important areas and intercept the enemy both on land and at sea.

Second, “avoid the enemy when they are highly motivated as a morning, fight them when they are exhausted as a late afternoon”. In their third invasion against Great Viet, Yuan Dynasty not only wanted to conquer our land and people, but also avenge the two previous crushing defeats. To ensure victory, before the invasion, Kublai Khan warned his generals: do not think that Giao Chi is an easy target; do not act rashly, do not be bitter, etc. However, having a strong army under his command, Prince Toghon became overconfident and hoped to capture Tran’s court to score a swift victory. Knowing the enemy’s intention and thanks to a comprehensive preparation as well as great confidence in the fighting spirit of our people, Tran Quoc Tuan decided to employ the stratagem “Wait at leisure when the enemy labour” in response to the Mongol. To “avoid the enemy when they are highly motivated as a morning”, he ordered main troops to withdraw, only left behind a small rearguard to slow down and entice the enemy into thinking that our force was weak. When the enemy attacked Thang Long Capital, “empty fortress strategy” was put in effect. The royal court and civilians were temporarily evacuated to Lower Red River. Unable to either capture our supreme command or destroy our main force while suffering significant loss, the enemy had to halt its offensive to solidify their gain. Our force began to launch minor skirmishes to harass the enemy and buy time for the main army to gather strength for a decisive counteroffensive.

Unable to achieve his objectives, being isolated and in constant fear of running out of supply, Toghon saw no way to continue to fight and decided to divide his force into land and seaborne contingents to withdraw, hoping to disperse our interception efforts. However, Tran Quoc Tuan correctly predicted the withdrawal plan and deployed our main naval force at Bach Dang Estuary to eliminate the enemy’s naval detachment and ordered militia forces to set up ambushes near the land border. Thanks to terrain advantages and with burning fighting spirit, our forces managed to completely destroy the enemy naval force on Bach Dang River and its land contingent at Noi Bang Passage. The fact that the retreating enemy’s situation was grim as a late afternoon allowed us to fight with only half of our strength but double the effectiveness; therefore, we succeeded in eliminating them both on land and at sea. According to Sun Tzu, “When you surround an army, leave an outlet free; do not press a desperate foe too hard”. However, to permanently disable the threat of further invasions, Tran Quoc Tuan decided to put aside this principle and dealt a decisive blow to the enemy on Bach Dang River.

Third, intercept, harass and destroy the enemy’s supply convoys. Supply is always vital to any expeditionary force. Learnt from the defeats of the two previous invasions, in which one of the main reason of the Mongol’s failure was food shortage, to feed his army of 300,000 troops, besides land-based supply line, Kublai Khan ordered Zhang Wenhu to transport 170000 Shis of food by ships. The escort for this convoy, which included 500 ships under the command of Omar, was also a naval offensive spearhead.  Understood the fact that cutting off the enemy supply line was critical, our force employed “empty fortress strategy” and launched attacks to destroy their supply convoys.

In late November 1287, the Mongol began its third invasion against Great Viet. After capturing Van Kiep, the enemy put great effort in enhancing their force to move forward Thang Long Capital. However, food shortage became a serious problem among its camps. Hence, the Mongol sent parties to loot supply from the population but often returned empty-handed due to our “empty farm, empty village” stratagem, some were even ambushed by our troops. In December 1287, Zhang Wenhu’s naval supply convoy and its escort, Omar’s fleet, left Qinzhou for our Northeast coast. Tran Khanh Du launched an unsuccessful interception attempt against this formation and had to retreat his force to fight another day. After evaluating the situation, Tran Khanh Du concluded: “Omar will become overconfident and rush to Van Kiep to converge with Toghon’s contingent, leaving supply ships behind - this is their fatal weakness”. Therefore, he set up an ambush and destroyed the enemy supply fleet. The outcome of this naval battle was: “Our force captured an innumerable amount of food and weapons and many prisoners of war”. Starved, sickened, and constantly ambushed by our force at every step, when the enemy heard about the destruction of their supply fleet, their morale completely collapsed. Meanwhile, the army of Tran Dynasty was still well-preserved in strength and ready to counterattack. It can be said that our victory at Van Don put the enemy into a very desperate situation, as Emperor Tran Nhan Tong commented: “The Yuan army heavily relied on their supply convoys, now they are captured by our troops, their formation cannot be stretched further; thus, we should release captured enemy troops, they will inform the news to Toghon, causing further morale loss, that makes them easier to be defeated”.

Stratagems that Tran Dynasty employed in the 3^rd Mongol Invasion are invaluable lessons that need to be further studied and applied for a possible patriotic war in the future.

Senior Colonel NGUYEN VAN THANH, PhD, The Infantry Officer College No.1