The Battle of Hanoi was fought on 20 November 1873 between France and Đại Nam. 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.
Background
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. Imperial authorities in Huế required from France that they took action to remove Dupuis from Bắc Kỳ.
Navy Lieutenant Francis Garnier was sent to Hanoi with two gunboats and 180 men in order to convince Dupuis to leave Bắc Kỳ and bring him back to Nam Kỳ. The small French force arrived to Hanoi on 5 November 1873. However, Garnier was soon very displeased with the way the local authorities treated him. After discussing with Dupuis, he became convinced that the trader's complains were justified while those of the Governor of Hanoi were not. When he attempted to discuss Dupuis' griefs with an Imperial mandarin, Garnier was told to know his place as a low ranking naval officer not habilitated to discuss important political matters. Forsaking his mission to bring back Dupuis, Garnier took the decision to capture the city.
Battle
Preparations
Garnier had tasked Second lieutenant of Marines Edgard de Trentinian with drawing a detailed map of the city's fortifications. For several days Trentinian walked along the walls, observing every detail, in order to draw something as accurate as possible. Garnier was very pleased with the young officer's work and used the map to carefully plan every single aspect of the city's storming.
A few days before the attack, Garnier strategically placed his two gunboats, Scorpion and Espingole, about 1,200 meters away from the walls. The ships had been anchored on a position he had deemed as being the best to fire on the citadel without being endangered by Vietnamese cannons. On 19 October, the guns of the ships had all been perfectly pointed to the specific targets chosen by Garnier. Due to most of the gunboats crews being needed on land for the storming, the ammunition for the ships guns were all gathered near the guns so that the gunners, the only men who would be left on the ships, would not waste any time to go fetch rounds.
On the eve of the attack, Lieutenant Garnier gathered the seven other officers of his expeditionary force: Ensign Charles Esmez (aged 26), Ensign Henri Bain (aged 28), Ensign Adrien Balny d'Avricourt (aged 24), Aspirant Marc Hautefeuille (aged 21), Aspirant Édouard Perrin (aged 21), Aspirant George Bouxin (aged 20) and Second lieutenant Edgard de Trentinian of the 4th Marine Infantry Regiment (aged 22). Garnier proceeded to meticulously explain to each of them his plan and what their own task was. Jean Dupuis insisted to take part in the storming with his Chinese mercenaries and, although very reluctant about it, Garnier eventually gave in.
Before going to sleep, Garnier wrote to his brother:
Storming of the city
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. A first column composed of 30 sailors and one cannon under the leadership of Ensign Bain left the camp at 5:30 am and stealthily moved toward the South-Western gate. Lieutenant Garnier left shortly afterward, alongside a second column composed of 27 marines under Second Lieutenant Trentinian and 48 sailors with 4 cannons under Ensign Esmez. This second column was directed toward the South-Eastern gate. A certain number of men, mostly sick ones, were left to guard the camp.