▁rivers ide ▁for ts , ▁and ▁squad s ▁of ▁engine ers ▁under ▁the ▁command ▁of ▁cap itaine ▁de ▁gén ie ▁Gall im ard ▁were ▁put ▁ash ore ▁to ▁burn ▁the ▁wooden ▁stock ades ▁that ▁linked ▁the ▁for ts . ▁ ▁The ▁Vietnam ese ▁def ended ▁themselves ▁vig or ously : ▁Drag onne ▁was ▁hit ▁with ▁three ▁can non ball s , ▁and ▁A val anche ▁by ▁seven . ▁ ▁The ▁inv aders ▁took ▁care ▁to ▁ensure ▁that ▁the ▁river ▁could ▁not ▁be ▁closed ▁behind ▁them . ▁ ▁After ▁each ▁fort ▁was ▁taken ▁its ▁can non ▁were ▁either ▁sp ik ed ▁or ▁taken ▁ab o ard ▁the ▁ships . ▁▁▁ ▁On ▁the ▁evening ▁of ▁ 1 5 ▁February ▁the ▁naval ▁division ▁( which ▁had ▁been ▁joined ▁in ▁the ▁river ▁by ▁the ▁des patch ▁vessel ▁Pr ég ent ) ▁arrived ▁in ▁view ▁of ▁the ▁two ▁for ts ▁built ▁by ▁Gia ▁Long ' s ▁French ▁engine ers , ▁which ▁def ended ▁Sa ig on ▁from ▁the ▁south . ▁ ▁During ▁the ▁night ▁two ▁armed ▁launch es ▁were ▁sent ▁forward ▁to ▁destroy ▁a ▁bar rage ▁made ▁of ▁boats ▁l ashed ▁together ▁and ▁filled ▁with ▁explos ives . ▁ ▁At ▁dawn ▁on ▁ 1 6 ▁February ▁Ph l ég é ton , ▁Prim au gu et , ▁Al ar me ▁and ▁A val anche ▁anch ored ▁ 8 0 0 ▁metres ▁from ▁the ▁for ts . ▁ ▁The ▁channel ▁was ▁so ▁narrow ▁that ▁Admir al ▁Char ner , ▁on ▁Ph l ég é ton ''' s ▁bridge ,