fleet devastated most of the naval force of General Trần Khánh Dư in Vân Đồn. Simultaneously, Prince Ariq-Qaya led his massive cavalry and captured Phú Lương and Đại Than garrisons, two strategic military posts bordering Đại Việt and China. The cavalry later rendezvous with Prince Toghan's navy in Vân Đồn. In response to the battle skirmish defeats at the hands of the Mongol forces, the Emperor Emeritus Trần Thánh Tông summoned General Trần Khánh Dư to be court-martialed for military failures, but the general managed to delay reporting to the court and was able to regroup his forces in Vân Đồn. The cavalry and fleet of Prince Toghan continued to advance into the imperial capital Thăng Long. Meanwhile, the trailing supply fleet of Prince Toghan, arriving at Vân Đồn a few days after General Trần Khánh Dư's had already occupied this strategic garrison, the Mongol supply fleet was ambushed and captured by General Trần Khánh Dư's forces. Khánh Dư was then pardoned by Emperor Emeritus. The Mongol main occupying army quickly realized their support and supply fleet has been cut off. The capture of the Mongol supply fleet at Vân Đồn along with the concurring news that General Trần Hưng Đạo had recaptured Đại Than garrison in the north sent the fast advancing Mongol forces into chaos. The Đại Việt forces unleashed guerrilla warfare on the weakened Mongol forces causing heavy casualties and destructions to the Yuan forces. However, the Mongols continued advancing into Thăng Long due to their massive cavalry strength, but by this time, the emperor decided to vacate Thăng Long to flee and he ordered the capital to be burned down so the Mongols wouldn't collect any spoils of war. The subsequent battle skirmishes between the Mongols and Đại Việt had mixed results: the Mongols won and captured Yên Hưng and Long Hưng provinces, but lost in the naval battles at Đại Bàng. Eventually, Prince Toghan decided to withdraw his naval fleet and consolidate his command on land battles where he felt the Mongol's superior cavalry would defeat the Đại Việt infantry and cavalry forces. Toghan led the cavalry through Nội Bàng while his naval fleet commander, Omar, directly launched the naval force along the Bạch Đằng River simultaneously. The Battle of Bạch Đằng River The Mongol naval fleet was unaware of the river's terrain. Days before this expedition, the Prince of Hưng Đạo predicted the Mongol's