A French expeditionary force composed of 140 sailors, 30 marines and 8 officers under the command of Navy Lieutenant Francis Garnier captured the provincial capital Hanoi, where they had been sent by France on a diplomatic mission, without superiors' orders.

The capture of the city became the starting point of an unsanctioned military campaign by Lieutenant Garnier and his men, who then proceeded to conquer most of the Bắc Kỳ region over the course of December 1873.

In late summer 1873, a dispute between French trader Jean Dupuis and the authorities of Hanoi was on the verge of causing a diplomatic crisis between France and Đại Nam.

In such case, I count on you to take care of Claire and my daughter".On the morning of 20 October, French troops woke up at 5:00 am and, after briefly eating some soup, they got ready for the attack which was planned for 6:00 am.

As the wall's cannons were placed en barbette rather than inside embrasures, the gunners were not protected and many of them fell to the deadly fire of French Chassepot rifles.

[14] Besides their low quality archaic rifles and cannons that they fired without accuracy, the defenders also used various extremely outdated tactics, such as throwing nails from the top of the walls in hope to harm the feet of the attackers, which quite perplexed the French whose military boots rendered the manoeuvre completely useless.

As soon as they heard the first sounds of the battle, the two gunboats unleashed a devastating artillery fire on the Northern and Western gates, as well as the portion of the wall in between them.

The sailors and marines, from covered positions, made use of a very effective suppressive fire on the defenders, while the cannons blew up the Vietnamese artillery pieces located on the fortification.

[16] Dupuis and 30 of his mercenaries, who were commanded by a Greek adventurer and veteran of the Ever Victorious Army named Georges Vlavianos, had been tasked with guarding the Eastern gate from outside to ensure no high ranking official would flee through there.

[21] To avoid any risk of desperate last stand action from their numerous cornered foes, the French took great care to explain them that they wouldn't be executed as prescribed for captured enemies by the local customs of warfare in the region at the time.

Then, with his 180 men and the two gunboats, he initiated a striking military campaign that resulted in the conquest of most of Bắc Kỳ between late November and December 1873.

[22] Despite being treated with respect by the French, General Tri Phương refused to have his wounds tended to and died on 20 December after undergoing a hunger strike.

Garnier was killed in action one day later on 21 December while pursuing, with 18 of his men, a 600-man strong Black Flag force he had just routed away from the city's walls with a cannonade.