elling ▁units ▁were ▁occupied ▁in ▁off ensive ▁and ▁def ensive ▁min ing ▁involving ▁the ▁placing ▁and ▁maintain ing ▁of ▁mines ▁under ▁enemy ▁lines , ▁as ▁well ▁as ▁other ▁under ground ▁work ▁such ▁as ▁the ▁construction ▁of ▁deep ▁d ug outs ▁for ▁tro op ▁accommod ation , ▁the ▁dig ging ▁of ▁sub ways , ▁s aps ▁( a ▁narrow ▁tren ch ▁d ug ▁to ▁approach ▁enemy ▁tren ches ), ▁cable ▁tren ches ▁and ▁ ▁under ground ▁ch amb ers ▁for ▁signals ▁and ▁medical ▁services . ▁ ▁Background ▁ ▁By ▁January ▁ 1 9 1 5 ▁it ▁had ▁become ▁evident ▁to ▁the ▁BE F ▁at ▁the ▁Western ▁Front ▁that ▁the ▁Germ ans ▁were ▁min ing ▁to ▁a ▁planned ▁system . ▁As ▁the ▁British ▁had ▁failed ▁to ▁develop ▁suitable ▁counter - t act ics ▁or ▁under ground ▁ ▁listening ▁devices ▁before ▁the ▁war , ▁field ▁mar sh als ▁French ▁and ▁K itch ener ▁agreed ▁to ▁investigate ▁the ▁suit ability ▁of ▁forming ▁ ▁British ▁min ing ▁units . ▁Following ▁consult ations ▁between ▁the ▁Engine er - in - Ch ief ▁of ▁the ▁BE F , ▁Brig ad ier ▁George ▁F ow ke , ▁and ▁the ▁min ing ▁special ist ▁John ▁N orton - Gr iff ith s , ▁the ▁War ▁Office ▁formally ▁approved ▁the ▁t unn elling ▁company ▁scheme ▁on ▁ 1 9 ▁February ▁ 1 9 1 5 . ▁ ▁N orton - Gr iff ith s ▁ens ured ▁that ▁t unn elling ▁companies ▁numbers ▁ 1 7 0 ▁to ▁ 1 7 7 ▁were ▁ready