Battle of Bang Bo (Zhennan Pass) - The Tonkin Military Stalemate, March 1885

The Tonkin Military Stalemate, March 1885

On 17 February 1885 General Louis Brière de l'Isle, the general-in-chief of the Tonkin Expeditionary Corps, left Lang Son with Lieutenant-Colonel Laurent Giovanninelli's 1st Brigade to relieve the Siege of Tuyen Quang. On 3 March, at the Battle of Hoa Moc, Giovanninelli's men broke through a formidable Chinese blocking position and relieved the siege. Before his departure Brière de l'Isle ordered General François de Négrier, who remained at Lang Son with the 2nd Brigade, to press on towards the Chinese border and expel the battered remnants of the Guangxi Army from Tonkinese soil. After resupplying the 2nd Brigade with food and ammunition, de Négrier defeated the Guangxi Army at the Battle of Dong Dang on 23 February and cleared it from Tonkinese territory. For good measure, the French crossed briefly into Guangxi province and blew up the 'Gate of China', an elaborate Chinese customs building on the Tonkin-Guangxi border. They were not strong enough to exploit this victory, however, and the 2nd Brigade returned to Lang Son at the end of February.

By early March, in the wake of the French victories at Hoa Moc and Dong Dang, the military situation in Tonkin had reached a temporary stalemate. Giovanninelli's 1st Brigade faced Tang Jingsong's Yunnan Army around Hung Hoa and Tuyen Quang, while de Négrier's 2nd Brigade at Lang Son faced Pan Dingxin's Guangxi Army. Neither Chinese army had any realistic prospect of launching an offensive for several weeks, while the two French brigades that had jointly captured Lang Son in February were not strong enough to inflict a decisive defeat on either Chinese army separately. Brière de l'Isle and de Négrier examined the possibility of crossing into Guangxi with the 2nd Brigade to capture the major Chinese military depot at Longzhou, but on 17 March Brière de l'Isle advised the army ministry in Paris that such an operation was beyond their strength. Substantial French reinforcements reached Tonkin in the middle of March, giving Brière de l'Isle a brief opportunity to break the stalemate. He moved the bulk of the reinforcements to Hung Hoa to reinforce the 1st Brigade, intending to attack the Yunnan Army and drive it back beyond Yen Bay. While he and Giovanninelli drew up plans for a western offensive, he ordered de Négrier to keep the Chinese in respect around Lang Son.

Meanwhile, behind the Chinese border, the Guangxi Army was also building up its strength. The French, whose Vietnamese spies in Longzhou had been conscientiously counting the company flags of every Chinese battalion that passed through the town, estimated on 17 March that they were facing a Chinese force of 40,000 men. This was an exaggeration, based on the assumption that each Chinese company was at full strength. In fact most of the Chinese commands were considerably understrength with 300 to 400 men, and the strength of the Guangxi Army at the Battle of Zhennan Pass was probably around a couple thousand men, while all of Longzhou had 25,000 to 30,000 men under arms. Even at this lower strength, it fearfully outnumbered the French.