At the end of 1881 Rivière was sent with a small French military force to Hanoi to investigate Vietnamese complaints against the activities of French merchants. In defiance of the instructions of his superiors, he stormed the citadel of Hanoi on 25 April 1882 in a few hours, with the governor Hoàng Diệu committing suicide having sent a note of apology to the emperor. Although Rivière subsequently returned the citadel to Vietnamese control, his recourse to force was greeted with alarm in both Vietnam and China.
