▁towards ▁the ▁A is ne ▁and ▁the ▁Franco - B rit ish ▁were ▁following - up , ▁collect ing ▁st rag gl ers ▁and ▁equipment . ▁On ▁ 1 2 ▁September , ▁J off re ▁ordered ▁an ▁out fl ank ing ▁move ▁to ▁the ▁west ▁and ▁an ▁attack ▁north wards ▁by ▁the ▁Third ▁Army , ▁to ▁cut ▁off ▁the ▁German ▁retre at . ▁The ▁purs uit ▁was ▁too ▁slow ▁and ▁by ▁ 1 4 ▁September , ▁the ▁German ▁arm ies ▁had ▁d ug ▁in ▁north ▁of ▁the ▁A is ne ▁and ▁the ▁Al lies ▁met ▁tren ch ▁lines , ▁rather ▁than ▁re arg u ards . ▁Front al ▁attacks ▁by ▁the ▁N inth , ▁Fif th ▁and ▁Six th ▁arm ies ▁were ▁rep uls ed ▁from ▁ ▁which ▁led ▁J off re ▁to ▁begin ▁the ▁transfer ▁of ▁the ▁Second ▁Army ▁west ▁to ▁the ▁left ▁fl ank ▁of ▁the ▁Six th ▁Army , ▁the ▁first ▁phase ▁of ▁the ▁operations ▁to ▁out fl ank ▁the ▁German ▁arm ies , ▁which ▁from ▁ 1 7 ▁September ▁to ▁ ▁moved ▁the ▁oppos ing ▁arm ies ▁through ▁Pic ard y ▁and ▁Fland ers , ▁to ▁the ▁North ▁Sea ▁coast . ▁ ▁First ▁Battle ▁of ▁the ▁A is ne , ▁ 1 3 – 2 8 ▁September ▁ ▁On ▁ 1 0 ▁September , ▁the ▁French ▁arm ies ▁and ▁the ▁BE F ▁advanced ▁to ▁explo it ▁the ▁victory ▁of ▁the ▁Mar ne ▁and ▁the ▁arm ies ▁on ▁the ▁left ▁fl ank ▁advanced , ▁opposed ▁only ▁by ▁re arg u