Between the pacification of Tonkin in the late 1880s and the Nghe-Tinh Soviet Movement of 1930–31, the Thai Nguyen Rebellion was the largest and most destructive anti-colonial uprising to occur in French Indochina. On August 31, 1917, an eclectic band of political prisoners, common criminals and mutinous prison guards seized the Thai Nguyen Penitentiary, the largest penal institution in northern Tonkin. From their base within the penitentiary, the rebels stormed the provincial arsenal and captured a large cache of weapons which they used to take control of the town. Anticipating a counterattack, the rebels fortified the perimeter of the town, executed French officials and Vietnamese collaborators and issued a proclamation calling for a general uprising against the colonial state. Although colonial forces retook the town following five days of intense fighting, mopping-up campaigns in the surrounding countryside stretched on for six months and led to hundreds of casualties on both sides.