the October engagements against the Guangxi Army, Brière de l'Isle took steps to resupply the western outposts of Hưng Hóa, Thái Nguyên and Tuyên Quang, which were coming under increasing threat from Liu Yongfu's Black Flags and Tang Jingsong's Yunnan Army. On 19 November, in the Battle of Yu-Oc, a column making for Tuyên Quang under the command of Colonel Jacques Duchesne was ambushed in the Yu-Oc gorge by the Black Flags but was able to fight its way through to the beleaguered post. The French also sealed off the eastern Delta from raids by Chinese guerillas based in Guangdong by occupying Tiên Yên, Đông Triều and other strategic points, and by blockading the Cantonese port of Beihai (Pak-Hoi). They also conducted sweeps along the lower course of the Red River to dislodge Annamese guerilla bands from bases close to Hanoi. These operations enabled Brière de l'Isle to concentrate the bulk of the Tonkin expeditionary corps around Chũ and Kép at the end of 1884, to advance on Lạng Sơn as soon as the word was given. The Lạng Sơn Campaign French strategy in Tonkin was the subject of a bitter debate in the Chamber of Deputies in late December 1884. The army minister General Jean-Baptiste-Marie Campenon argued that the French should consolidate their hold on the Delta. His opponents urged an all-out offensive to throw the Chinese out of northern Tonkin. The debate culminated in Campenon's resignation and his replacement as army minister by the hawkish General Jules Louis Lewal, who immediately ordered Brière de l'Isle to capture Lạng Sơn. The campaign would be launched from the French forward base at Chũ, and on 3 and 4 January 1885 General de Négrier attacked and defeated a substantial detachment of the Guangxi Army that had concentrated around the nearby village of Núi Bop to try to disrupt the French preparations. De Nègrier's victory at Núi Bop, won at odds of just under one to ten, was regarded by his fellow-officers as the most spectacular professional triumph of his career. It took the French a month to complete their preparations for the Lạng Sơn Campaign. Finally, on 3 February 1885, Brière de l'Isle began his advance from Chũ with a column of just under 7,200 troops, accompanied by 4,500 coolies. In ten days the column advanced to the outskirts of Lang Son. The troops were burdened with the weight of their