Dongguan and cutting it off from the road to Yunnan. When Ming soldiers were recalled from Vinh to reinforce Dongguan, Lê Lợi, leaving some troops to besiege Vinh, followed the Ming forces as they moved north, rallying thousands of men from Thanh Hoa as he went. Pushing into the Red River Delta he proclaimed as king a certain Trần Cảo, supposedly a Trần prince. Men and scholars from the Red River Delta began to join his army as he called for those who had favored the Ming to come to his side and arrested those who did not. The Chinese general, Wang Tong, at Dongguan as Huang Fu's replacement, was prepared to surrender, but local people who were loyal to Ming persuaded him to resist. Civilians in the Red River Delta welcomed and supported the Lam Son army where they came. In early December 1426, Lý Triện and Đinh Lễ's 3,000 Vietnamese rebels achieved a surprise victory over the Ming army led by Wang Tong with about 30,000 Chinese soldiers were killed or captured in Tốt Động (32 km south of Hanoi) while countless horses, supplies, weapons, and so on fell into Vietnamese hand. Among these Ming troops were 510 soldiers armed with firearms, led by the regional military commander of the Firearms Battalion, Xie Rong, whom had been sent on May 8, 1426, by the Ming emperor to follow Wang Tong. By 1427, captured northern and Muslim prisoners also furnished the Vietnamese with siege techniques, primitive tanks, flying horse carts, Muslim trebuchets (hui hui pao 回回砲), and another artillery piece that the Chinese called a "thousand-ball thunder cannon". By the beginning of 1427, five major Ming strongholds were under siege. These were Dongguan and Tây Đô; Cổ Long, a fortress built to guard the southern entrance to the Red River delta in Y Yen district, near Vu Ban in Nam Định Province, on the road between Dongguan and Tây Đô; a fortress at Chí Linh, near Phả Lại, that guarded the eastern part of the Red River delta; and Xương Giang, a citadel at the modern city of Bắc Giang that guarded the route out of the Red River Delta to the northern border. All the Ming garrisons south of Tay Do had surrendered. Lê Lợi established his headquarters at Bồ Đề, in Gia Lâm district, directly across the Red River from Dongguan. Final victories In late March 1427,