A modern fortified post, with abundant and relatively powerful armament (81 mortars and 75 cannons), Dong Dang was held by a strong company (170 men including 30 Europeans). Connected by telephone to Lang Son and Nacham, the station also has a radio link.
On the 9th, during the day, given the visible increase in Japanese troops and the alert of the previous day, Battalion Commander Soulié had the fort guarded by the security garrison, the rest of the personnel occupying the barracks.
The attack was triggered around 9 p.m. by violent artillery fire. It shortly precedes
a first enemy assault, which will be repelled. During the night, the Japanese managed to infiltrate the post, but they were dislodged by an exit from the garrison. Commander Soulié is killed. During the day of the 10th, the Japanese moved away but blocked the garrison with harassing fire.
The attackers resume the attack with the night and are repulsed with heavy losses. On the morning of the 11th, the Japanese surrender offer was refused by Captain Annosse.
The assaults resumed and lasted all night from the 11th to the 12th. The resistance of the garrison weakened, many weapons were destroyed by Japanese fire. At dawn, the adversary managed to gain a foothold on the fort. Ammunition ran out. Captain Annosse then agrees to return the fort. He will be congratulated, as well as his men, by the Japanese general who led the attack, then executed with about fifty survivors. They will be stripped, taken to the edge of the passive defense trenches, forced to kneel and beheaded. The wounded are finished off with bayonets.
Three survivors manage to get out of the mass grave — Private Cron and two skirmishers, seriously wounded. With the help of the inhabitants, they will join a French detachment:Private Cron will arrive in China and the skirmishers will return to their villages.