Pigneau's expedition left for Vietnam on 19 June 1789 and arrived at Vũng Tàu on 24 July 1789. The foreign contingent helped to consolidate southern Vietnam and modernized its army, navy and fortifications. Olivier de Puymanel, a former officer of the "Dryade" who has deserted in Poulo Condor, built in 1790 the Citadel of Saigon and in 1793 the Citadel of Diên Khánh according to the principles of Vauban. He also instructed Vietnamese troops in the modern use of artillery, and implemented European infantry methods in the Vietnamese army of Nguyễn Phúc Ánh. Puymanel is said to have trained the 50,000 men of Nguyen's army. French bombs were used at the siege of Qui Nhơn in 1793.