At heavy cost, Colonel Giovanninelli's 1st Brigade of the Tonkin Expeditionary Corps defeated forces of the Black Flag and Yunnan Armies blocking the way to the besieged French post of Tuyên Quang.

The Tuyên Quang garrison, 400 legionnaires and 200 Tonkinese auxiliaries under the command of chef de bataillon Marc-Edmond Dominé, beat off all attempts to storm their positions, but lost over a third of their strength (50 dead and 224 wounded) sustaining a heroic defence against overwhelming odds.

Following his capture of Lạng Sơn on 13 February 1885, General Louis Brière de l'Isle personally led Colonel Giovanninelli's 1st Brigade to the relief of Tuyên Quang.

The brigade left Lạng Sơn on 17 February, after replenishing its food and ammunition, and made a forced march back to Hanoi along the Mandarin Road, via Cut, Thanh Moy, Cau Son and Bắc Lệ.

The brigade was reinforced at Phu Doan on 24 February by two ad hoc infantry battalions (1,000 men) drawn from the garrisons of Sơn Tây and Hưng Hóa.

The French knew that the Chinese and Black Flags had established a strong blocking position in the Yu Oc gorge, near the village of Hòa Mộc.

In theory, the French column could have avoided this blocking position by advancing northwest along the Song Chay river and approaching Tuyên Quang from the west.

Even if the flank march succeeded, the column would still have to fight its way through the Yunnan Army's siege lines around Ca Lanh or Phu An Binh, and these were reported to be as well-defended as the Hòa Mộc position.

Brière de l'Isle and Giovanninelli therefore decided to advance directly on Tuyên Quang through the Yu Oc gorge, forcing the defences of Hòa Mộc.

On 28 February the brigade crossed the Song Chay river and camped 5 kilometres (3.1 mi) below the village of Hòa Mộc, at the entrance to the Yu Oc gorge.

The Chinese and Black Flag forces blocking the way to Tuyên Quang were under the personal command of Liu Yongfu (Luu Vĩnh Phúc, as he was known to the French from the Vietnamese pronunciation of his name), and seem to have numbered around 6,000 men.

According to Lieutenant Huguet of Lambinet's marine infantry battalion, both Brière de l'Isle and Giovanninelli had been shaken by the ferocity of the enemy's resistance and were contemplating the possibility of defeat: The general-in-chief was sitting behind a bank, anxious, his head in his hands, surrounded by his staff, perhaps wondering whether he would have to retreat.

Colonel Giovanninelli, who valued the life of the humblest soldier as dearly as his own, was pale and shaken as he watched the lines of bloodstained stretchers file past him, and kept exclaiming in a strangled voice, 'My children!

[4] During the night of 2 March the Chinese and Black Flags made a counterattack in an attempt to recover the trenches they had lost, but were met with the bayonet by Comoy's Turcos and driven off after vicious hand-to-hand fighting.

Its casualties in the Battle of Núi Bop (4 January 1885) and during the Lạng Sơn Campaign (February 1885) had been relatively light, but after Hòa Mộc it could only muster 307 men and 6 officers.

'[6] The French public did indeed applaud chef de bataillon Marc-Edmond Dominé's defence of Tuyên Quang, and it eventually became the defining image of the Sino-French War in France.

They took what comfort they could from the order of day issued by Brière de l'Isle to the 1st Brigade on 5 March 1885: Vous venez d'ajouter une glorieuse page à l'histoire du corps expéditionnaire.

Le 2 mars, vous avez rencontré l'armée chinoise, descendue du Yun-Nan, retranchée dans une série d'ouvrages formidables, sur un terrain d'une difficulté inouïe.