In the second half of February General Louis Brière de l'Isle, the general-in-chief of the Tonkin Expeditionary Corps, returned to Hanoi with Lieutenant-Colonel Laurent Giovaninelli's 1st Brigade to relieve the Siege of Tuyên Quang, leaving General François de Négrier at Lạng Sơn with the 2nd Brigade.

Meanwhile, the French government was pressuring Brière de l'Isle to send the 2nd Brigade across the border into Guangxi province, in the hope that a threat to Chinese territory would force China to sue for peace.

Substantial French reinforcements reached Tonkin in the middle of March, giving Brière de l'Isle a brief opportunity to break the stalemate.

While he and Giovanninelli drew up plans for a western offensive, he ordered de Négrier to hold his positions at Lạng Sơn.

On 23 and 24 March the 2nd Brigade, 1,500 men strong, battled Guangxi Army troops entrenched near Zhennanguan on the Chinese border.

As the brigade's morale was precarious and ammunition was running short, de Négrier decided to fall back to Lạng Sơn.

Shortly before noon the Chinese launched a frontal attack on the French positions, advancing in dense, ponderous columns.

De Négrier ordered Lieutenant-Colonel Paul-Gustave Herbinger to counterattack the Chinese left wing with Diguet and Farret's battalions.

The attack, supported by artillery, was completely successful, and by 4:00 pm Herbinger had driven the Guangxi Army's left wing from the hills to the northeast of Ky Lua.

[2][3][4][5][6][7][8][9] Herbinger was a noted military theoretician who had won a respectable battlefield reputation during the Franco-Prussian War, but was quite out of his depth as a field commander in Tonkin.

Several French officers had already commented scathingly on his performance during the Lạng Sơn campaign and at Bang Bo, where he had badly bungled an attack on the Chinese positions.

Disregarding the appalled protests of some of his officers, he ordered the 2nd Brigade to abandon Lạng Sơn on the evening of 28 March and retreat to Chu.

The retreat to Thanh Moy and Dong Song was conducted without loss and without interference from the Chinese, but both Herbinger and Schoeffer set an unnecessarily punishing pace, and both halves of the brigade were exhausted by the time they reached their destinations.

His immediate reaction, on the evening of 28 March, was to despatch a pessimistic cable back to Paris which would have momentous political consequences two days later.

On 30 March the French threw up field defences at Thanh Moy and Dong Song and prepared to meet the advancing Chinese, while Herbinger sent out cavalry patrols to determine the exact positions of the Guangxi Army.

The patrols observed small Chinese scouting parties near Cut on the Mandarin Road and at Pho Bu, just to the south of Lạng Sơn, and duly reported their presence.

Herbinger wildly exaggerated the significance of these reports, and warned Brière de l'Isle that, in his opinion, the brigade faced catastrophic encirclement.

Shortly after dawn on 31 March Chinese skirmishers caught up with the French column near the small village of Pho Cam.

On 29 March, while the French were retreating southwards, the demoralised Chinese were streaming back towards Zhennanguan, heading for the shelter of their entrenched camps at Bang Bo and Yen Cua Ai.

Vietnamese sympathisers caught up with the Chinese near Cua Ai on the evening of 29 March, bringing the astonishing news that the French had abandoned Lạng Sơn and were in full retreat.

The Chinese general Pan Dingxin promptly turned his battered army around and reoccupied Lạng Sơn on 30 March.

The main body of the Guangxi Army was in no condition to pursue the French to Chu, and Pan contented himself with a limited advance to Dong Song and Bắc Lệ.

Ferry's immediate reaction was to reinforce the army in Tonkin, and indeed Brière de l'Isle quickly revised his estimate of the situation and advised the government that the front could soon be stabilised.

China, for its part, had suffered a major defeat at the hands of the French navy on 31 March (a development that received little attention in metropolitan France), and was also wary of a possible war with Japan over their competing interests in Korea.

Brière de l'Isle was understandably furious at Herbinger's conduct, and a commission of enquiry was held in Hanoi during the autumn of 1885 to determine whether his decision to abandon Lạng Sơn had been justified.

Most of the officers of the Tonkin expeditionary corps believed that Herbinger had made a ghastly mistake, and would have been happy to see him broken and dismissed from the service.