Vũ Văn Dũng

At first, Vũ Văn Dũng was subordinate of Phạm Ngô Cầu (the administrator of Phú Xuân, appointed by a trịnh lord).

After Nguyễn Quang Toản became emperor at age 9, his new regent Bùi Đắc Tuyên replaced Dũng with general Ngô Văn Sở and sent the former back to Phú Xuân.

Dũng, Phạm Công Hưng, and Nguyễn Văn Huấn besieged the regent's house, arrested him, and imprisoned him.

Dũng then ordered Nguyễn Quang Thùy to arrest Sở in Tonkin, while Huấn was sent to Quy Nhơn to capture Tuyên's son Bùi Đắc Trụ.

Sở, Trụ, and Tuyên were taken to Phú Xuân, where they were executed by being drowned in the Perfume River in front of emperor Toản, who could do nothing but weep.

Toản was afraid that a civil war might break out at any moment, and sent an army led by Dũng and Nguyễn Văn Danh to defend against Diệu in case he attacked.

Dũng was granted the position Đại tư đồ (大司徒 "Grand Minister Over the Masses"), and became a regent along with Diệu, Huấn, and Danh.

Two Nguyễn generals, Võ Di Nguy and Lê Văn Duyệt, were sent as vanguards to attack the Tây Sơn navy.

[1][2] An army of 30 thousand men under the boy-emperor marched south to recapture the lost territory, but were badly defeated in a battle at the mouth of Nhật Lệ River.