The Battle of Bạch Đằng was a decisive naval battle during the third Mongol invasion of Vietnam between Đại Việt commanded by Commander-in-Chief Prince Trần Quốc Tuấn (Prince Hưng Đạo),[2] and the fleet of the Yuan dynasty, commanded by Admirals Omar and Fan Yi on the Bạch Đằng River (today Quảng Ninh province), which Prince Hưng Đạo staged an ambush that destroyed the Yuan fleet, capturing its general, ending Kublai’s intention to conquer Dai Viet and Champa.

[4] In March 1284 he and Qutuq (Mongol commander in a battle against the Burmese in 1277) had been accompanied to lead some 20,000 troops to join Sogetu against Champa, but he eventually went north to assist prince Toghon in the Yuan invasion of Dai Viet in early 1285,[5] where he and the Tangut prince Li Heng used captured warships and drove the Vietnamese king Tran Nhan Tong to the sea in March.

Sogetu was killed in battle soon after while Omar and his companion Liu Gui were successfully escaping to the beach, found a small boat, and sailed back to China.

They assaulted, drove the king to the sea, and captured the Viet capital Thang Long (Hanoi) on 3 February, but found no grain left to resupply.

[9] The Yuan army was large, unsustainable, and was waiting for the supply fleet, commanded by Zhang Wenhu, slowly sailing toward Dai Viet.

[11] Meanwhile, the Yuan fleet commanded by Omar and Fan Yi retreated through the Bạch Đằng river, the same route previously where they entered Dai Viet.

[10] The Bạch Đằng River ran through Yen Hung district (in Quảng Ninh province) and Thuy Nguyen (in Hai Phong) before reaching the sea.

He studied the tidal lore, and ordered beds of stakes to be planted under the water and arranged ambushes in a unified plan of campaign.

Trần Hưng Đạo ordered his soldiers to nail the iron-headed poles under the waters of the Chanh, Kênh and Rút rivers.

In the early morning of 9 April, the naval fleet led by Omar, and escorted by infantry, fled home along the Bạch Đằng river.

Then the tide receded, with the Yuan fleet pursuing and battling the Vietnamese junks, revealing wooden stakes that had been planted into the river bed.

Kublai's successor Temür Khan (r. 1294–1307), finally released all detained envoys, settling instead for a nominate tributary relationship, which continued until the end of the Yuan dynasty.