 The Messines defences were on a forward slope , overlooked from Haubourdin Hill ( Hill 63 ) south of the Douve valley and Kemmel Hill , 5 @,@ 000 yards ( 4 @,@ 600 m ) west of Wijtschate , an arrangement which the experience of 1916 showed to be obsolete . A new line incorporating the revised principles of defence derived from the experience of the Battle of the Somme , known as Flandern I , was begun in February 1917 . The first section began 6 miles ( 9 @.@ 7 km ) behind Messines Ridge , running north from the Lys to <unk> then <unk> and <unk> , where the nearest areas giving good artillery observation to the west were found . In April , Field Marshal Crown Prince Rupprecht and his chief of staff , Lieutenant @-@ General Hermann von Kuhl , favoured withdrawal to the Warneton ( third ) line , before a British attack . The local divisional commanders objected , due to their belief that counter @-@ mining had neutralised the British underground threat and the inadequacy of the Warneton line . The convex eastern slope limited artillery observation and the Ypres – Comines canal and the river Lys restricted the space below the ridge where infantry could manoeuvre for counter @-@ attacks . British observation from the ridge would make the ground to the east untenable as far as Flandern I 6 miles ( 9 @.@ 7 km ) beyond . A withdrawal that far would uncover the southern slopes of Menin Ridge , which was the most vital part of the Flandern position . Rupprecht re @-@ examined the Warneton ( third ) line and the extra Sehnen line ( Oosttaverne line to the British ) between the Warneton Line and the <unk> ( second ) line and dropped the withdrawal proposal . 
