Two hundred and forty years ago, during the war against the Siamese invasion, the Tay Son insurgent forces, together with the local populace, annihilated and captured over 40,000 enemy soldiers, leaving only a few thousand remnants to retreat back to their homeland. This resounding victory shattered Siam’s ambitions of invading our country, marking a glorious milestone in our nation’s history of resistance against foreign aggression and providing invaluable lessons in the art of warfare in riverine environments.

The war against the Siamese invaders unfolded against the backdrop of the Tay Son insurgents’ recent consolidation of the southern region. This period was marked by both advantages and challenges. Notably, to achieve the strategic goal of gaining control over the southern region, Nguyen Hue had previously employed shrewd diplomatic measures to hold the Trinh forces in check in Thuan Hoa (the northern region), enabling him to concentrate military efforts on subjugating the southern region. This was achieved through five strategic offensives (in 1776, 1777, 1778, 1782, and 1783), which effectively dismantled the Nguyen dynasty’s ruling apparatus and established a new administrative system. By the end of 1783, the Nguyen forces had been thoroughly defeated by the Tay Son, left without refuge, and forced to flee. In desperation, they sought the Siamese king’s assistance, shamefully “Let the fox guard the hen house,” resulting in an indelible national disgrace. Seizing this rare opportunity, and driven by territorial expansionist ambitions, the Siamese king promptly mobilised an elite force of 50,000 soldiers to invade our country. Guided by the remnants of Nguyen Anh’s troops, the Siamese forces advanced in coordination. In July 1784, they divided into three contingents: two infantry divisions, totalling 30,000 troops under the command of Sa Uean and Chiao Chui Ben, crossed through Khmer territory to attack from the southwestern border; meanwhile, the naval division, led by Chiao Tang and Chiao Suang, advanced via the sea to assault the southern coastline of our country.

In response to this invasive onslaught, Nguyen Hue, with his unparalleled military acumen, along with the Tay Son High Command, accurately assessed all aspects of the situation, particularly the enemy’s strength, the terrain, and the advantages and challenges of combat in the riverine environment. Based on this analysis, they decided against a direct assault on the Siamese naval headquarters in Sa Dec. Instead, they cunningly lured the enemy out of their stronghold to a pre-selected area, where they concentrated their forces to deliver a decisive, pivotal battle that would end the war.

The victory over the Siamese invaders, culminating in the monumental battle of Rach Gam - Xoai Mut, stands as a brilliant achievement and a source of immense national pride. This exemplary engagement, distinguished by its unique features of riverine military strategy, remains a paragon of warfare on riverine terrain.

The Rach Gam - Xoai Mut Victory Monument

1. Adopting a rational combat strategy suited to the situation, terrain, and force comparison. This was crucial issue in the early stages of the war against the Siamese invasion to avoid significant losses, maintain control of key areas and strategic positions, and establish a foundation for transitioning to counteroffensive and offensive operations when the opportunity arose, ultimately securing final victory.

At the beginning of August 1784, only a month after launching their invasion, the Siamese forces - advantaged by their superior numbers and assisted by Nguyen Anh’s betrayal - had overrun Kien Giang, Tran Giang (Can Tho), Ba Thac (Soc Trang), Dong Khau (Sa Dec), Tra On (Vinh Long), and other areas with minimal resistance. Exploiting their successful advance, they dispersed their forces across multiple directions and territories, aiming to quickly seize the entire western Gia Dinh region, then move towards eastern Gia Dinh, with their primary axis of attack being My Tho - Gia Dinh. At this time, the Tay Son’s main forces were stationed in the north and had not yet mobilised south to confront the enemy. Local forces in the area were insufficient to achieve victory in a direct confrontation with the Siamese, given the disparity in strength. Consequently, the Tay Son adopted a rational and prudent combat strategy. They deployed a portion of their forces to hold and counter the enemy at critical locations, aiming to deplete their strength and slow their advance. Simultaneously, the majority of their troops were concentrated on defending the strategically vital areas of Gia Dinh Citadel and eastern Gia Dinh. This defensive posture created a solid foundation to preserve their positions and forces while buying time for reinforcements to arrive from the north. This approach successfully thwarted the enemy’s objective of a swift and decisive victory. The Siamese suffered considerable losses and were forced to pause their advance to regroup and prepare for further offensives. By December 1784, despite their initial momentum, they had managed to capture only a few additional areas, including Xu Lach (Cho Lach - Ben Tre), Long Ho (Vinh Long), Tra Lot, and Tra Tan (on the Tien River). By employing a well-suited combat strategy, the Tay Son forces effectively restrained the Siamese advance, creating favourable conditions for their naval forces to mobilise and establish positions in My Tho in preparation for engagement. Nevertheless, the Siamese remained numerically and militarily superior, maintaining the strategic offensive. Confronting them head-on or launching an immediate attack against their stronghold at Tra Tan would have risked substantial losses or even outright failure. Even a victory in such circumstances would have been costly and far from optimal. Based on a thorough analysis of the situation and the strengths of both sides, Nguyen Hue determined that success would require a combination of “strength” and “wisdom.” He emphasised the need to harness comprehensive power and creatively leverage the key elements of combat - ”force, position, timing, and strategy” - to achieve a decisive and complete victory. The outcome of the battle of Rach Gam - Xoai Mut vividly demonstrated the effectiveness of this approach, as the Tay Son forces annihilated the invaders and collaborators, safeguarding the nation’s sovereignty.

2. Selecting a favourable battlefield and resolutely attacking to secure a decisive victory. Upon leading his main forces to My Tho, Nguyen Hue seized the opportunity to swiftly prepare for battle. This included reorganising his troops, conducting reconnaissance to assess the enemy’s situation (their numbers, positions, and primary axes of attack), and studying the terrain (local population, geography, soil, tides, etc.). Based on this intelligence, he devised a combat strategy suited to the conditions of fighting a numerically superior enemy. From the outset, the Tay Son forces adhered to the principle of decisively attacking and annihilating the enemy, despite their disadvantages in strength, to bolster morale and galvanise their determination to fight against the invaders. With this strategy in mind, Nguyen Hue and the Tay Son High Command aimed to organise a decisive, strategic battle to completely defeat the enemy, end the war swiftly, and minimise losses - adopting a “quick strike, swift victory” approach. This was a profoundly wise decision by Commander Nguyen Hue, as the Tay Son forces faced a precarious situation. Not only were they contending with the Siamese invasion, but the Trinh forces, who were poised in Thuan Hoa, remained a looming threat and could attack the south at any moment; the peace agreement with them was only temporary. Prolonging the war against the Siamese would have jeopardised the broader strategic situation. Moreover, Nguyen Hue’s hallmark of rapid, surprise attacks to decisively annihilate large enemy forces in a single battle - a method later exemplified in his legendary campaign against the Qing in 1789 - was a defining feature of his military genius.

The most critical factor for ensuring success in a decisive battle was selecting a battlefield that would play to the Tay Son’s strengths and maximise the combined power of their forces, enabling them to “establish our advantage and destroy the enemy’s position.” After carefully analysing all aspects of the situation, the Tay Son High Command decided to stage the ambush along a stretch of the Tien River between Rach Gam and Xoai Mut. This section, approximately 7 kilometres long and 1 to 2 kilometres wide, lay close to My Tho. The location allowed the Tay Son to exploit tidal flows and wind conditions, strategically block the enemy fleet, and concentrate their forces to destroy hundreds of large enemy warships in a single engagement. By deploying elite naval forces at Rach Gam and Xoai Mut, the Tay Son created two highly effective assault points, enabling them to block the enemy at both the front and rear. This strategy disrupted and immobilised the Siamese-Nguyen fleet, rendering it vulnerable to devastating attacks. The middle section of the Tien River, between Tra Lot and My Tho, featured numerous islands of varying sizes, dense vegetation along the riverbanks, and sparse populations - ideal conditions for concealing ambush forces and positioning artillery. These features enabled the Tay Son to establish a solid and formidable defensive position. The battle unfolded precisely according to plan. Within a single day, the Tay Son forces annihilated the entire Siamese-Nguyen naval contingent.

3. Identifying a suitable method of combat and leveraging the combined power of all forces, with close coordination between the navy, artillery, and infantry, exploiting opportunities and ending the war in the most advantageous manner. The Tay Son High Command’s decision to adopt an ambush strategy for the decisive battle was a judicious choice. This approach fully capitalised on the advantages of the terrain, maximised the strengths of the navy, infantry, and artillery, and created a synergistic force that overwhelmed the enemy, leaving them no time to respond or counteract effectively.

In preparation for the decisive battle, Nguyen Hue not only ensured logistical readiness and adjusted troop deployments but also employed psychological and diplomatic tactics. He sent envoys to negotiate a separate ceasefire with Chiao Tang and Chiao Suang, feigning submission to lull the Siamese commanders into a false sense of security and sow distrust and division within the Siamese-Nguyen alliance. Believing that the Tay Son sought only peace, the Siamese became complacent, and, seizing the perceived opportunity, launched an offensive aimed at annihilating the Tay Son’s main forces in My Tho. On the night of 19 January 1785, timing their movement with tidal flows, water currents, and wind directions, the Siamese fleet advanced en masse towards My Tho. Nguyen Hue, anticipating this move, implemented his pre-planned ambush strategy, later lauded as one of the most brilliant manoeuvres in military history. As the enemy fleet approached Rach Gam, a small contingent of Tay Son ships launched a diversionary attack before feigning retreat towards Xoai Mut, drawing the Siamese forces into the ambush zone. By dawn the following day, the entire Siamese fleet had entered the trap, their vessels tightly clustered together. At the opportune moment, Tay Son artillery, strategically positioned on both riverbanks and the islands, unleashed a devastating barrage on the Siamese ships. Simultaneously, elite naval units from My Tho advanced in two formations along either side of Thoi Son Island, encircling and cutting off the enemy’s escape routes. This combined assault devastated the Siamese fleet, shattering their forces. Capitalising on the momentum of their victory, the Tay Son navy and infantry launched a coordinated offensive against enemy fortifications from Tra Tan to Tra Lot. News of the naval defeat threw the Siamese infantry into disarray. Overwhelmed by fear and confusion, most were swiftly annihilated or captured by the advancing Tay Son forces.

The resounding victory at Rach Gam - Xoai Mut exemplified the extraordinary strategic acumen of Nguyen Hue and the Tay Son High Command. Their ability to creatively and flexibly apply military principles in combat on riverine terrain underscored their unparalleled prowess. Though the war is now a distant memory, the remarkable aspects of the Tay Son’s riverine combat strategy endure as invaluable lessons. These insights continue to merit study and adaptation to modern contexts, serving as a testament to the enduring legacy of the nation’s struggle to safeguard its sovereignty.

MANH HA