Bombardment of Tourane The Bombardment of Tourane ( 15 April 1847 ) was a naval incident that took place during the short reign of the Vietnamese emperor Thiệu Trị ( 1841 – 47 ) , which saw a considerable worsening of relations between France and Vietnam . The French warships " Gloire " and " Victorieuse " , which had been sent to Tourane ( now Da Nang ) to negotiate for the release of two French Catholic missionaries , were attacked without warning by several Vietnamese vessels . The two French ships fought back , sinking four Vietnamese corvettes , badly damaging a fifth , and inflicting just under 1 , 200 casualties . In response to this and other provocations , the French eventually decided to intervene actively in Vietnam , and a decade later launched the Cochinchina Campaign ( 1858 – 62 ) , which inaugurated the period of French colonial rule in Vietnam . Background . French missionaries had been active in Vietnam since the seventeenth century , and by the middle of the nineteenth century there were perhaps 300 , 000 Catholic converts in Annam and Tonkin . Most of their bishops and priests were either French or Spanish . Most Vietnamese disliked and suspected this sizeable Christian community and its foreign leaders . The French , conversely , began to feel responsible for their safety . During the reigns of the Vietnamese emperors Minh Mạng ( 1820 – 41 ) and Thiệu Trị ( 1841 – 47 ) , Catholic missionaries were forbidden to live and work in Vietnam , and several European missionaries who ignored this edict were either banished or , on occasion , executed . French naval captains in the Far East were given instructions to negotiate with the Vietnamese authorities when such cases occurred . On two occasions they intervened with considerable success . On 25 February 1843 , " capitaine de frégate " Favin - Lévêque , captain of the French warship " Héroine " , anchored off Da Nang to intercede for the release of five missionaries detained at Huế for two years . After long and frustrating negotiations , the five missionaries were released . In 1845 , the French corvette " Alcmène " ( " capitaine de frégate " Fornier - Duplan ) went to Tourane to ask for the release of Dominique Lefèbvre , the French vicar apostolic of Lower Cochinchina , who was being held prisoner at Huế . Again , the Vietnamese acceded to the French request , and Lefèbvre was released . Bombardment . The 1845 intervention was ordered by Admiral Cécille , the senior French naval officer on station . In 1847 , Dominique Lefèbvre secretly re - entered Vietnam . He and another missionary , Duclos , were imprisoned . The arrest of the two missionaries provoked a further confrontation between the Vietnamese rulers and the ships of the French Navy charged with protecting the interests of Roman Catholic missionaries in Vietnam . In March 1847 , Cécille sent the 54 - gun frigate " Gloire " ( " capitaine de vaisseau " Augustin de Lapierre ) and the 24 - gun corvette " Victorieuse " ( " capitaine de frégate " Charles Rigault de Genouilly ) to Tourane , with instructions to negotiate for the liberation of the two imprisoned French missionaries and to seek a commitment from the Vietnamese authorities to allow freedom of worship for Roman Catholics in Vietnam . Probably because the Vietnamese considered Lefèbvre ' s return to Vietnam a deliberate provocation by the French , the negotiations failed . Discussions dragged on without result , and on 15 April 1847 six Vietnamese corvettes attacked the two French ships in the Bay of Tourane . In the brief action that followed , the French sank four Vietnamese corvettes and disabled a fifth , and inflicted nearly 1 , 200 casualties on the outclassed Vietnamese sailors . According to the French , the Vietnamese spun out the negotiations to win time to assemble a fleet , and then treacherously attacked the two French warships without warning . Colonel Alfred Thomazi , the historian of the French conquest of Indochina , also claimed that the Vietnamese first attempted to lure the French officers to their deaths : Thomazi gave the following description of the battle in Tourane Bay : Lefèbvre was released by the Vietnamese authorities either before or shortly after the battle ( the sources differ ) . Significance . The Vietnamese naval defeat at Tourane dramatically demonstrated the technological superiority of the French warships over the antiquated vessels of the Vietnamese fleet . In the eyes of many thoughtful Vietnamese , it demonstrated that the kingdom ' s blind adherence to the values and traditions of the past had left it painfully vulnerable to European coercion , and spurred calls for modernization . Harassment of the Christians eventually provided France with a pretext for attacking Vietnam . The tension built up gradually . During the 1840s , the persecution of Roman Catholic missionaries in Vietnam evoked only sporadic and unofficial French reprisals , such as that taken by de Lapierre and Rigault de Genouilly in 1847 . In 1857 , however , the execution of two Spanish Catholic missionaries by the emperor Tự Đức led directly to French intervention in Vietnam . In September 1858 , a joint French and Spanish naval expedition landed at Da Nang . Its commander was Admiral Charles Rigault de Genouilly , one of the two French naval captains involved in the 1847 incident . The resultant Cochinchina campaign inaugurated the era of French colonial rule in Vietnam .