th ▁T unn elling ▁Company , ▁d ug ▁deep ▁gall eries ▁over ▁four ▁months ▁during ▁the ▁winter ▁and ▁in ▁late ▁February , ▁three ▁mines ▁were ▁placed ▁under ne ath ▁the ▁shall ower ▁gall eries ▁d ug ▁by ▁the ▁Germ ans . ▁An ▁attack ▁was ▁prepared ▁by ▁the ▁ 1 2 th ▁Division ▁for ▁ 2 ▁March , ▁to ▁re capt ure ▁The ▁Ch ord . ▁The ▁mines ▁were ▁spr ung ▁at ▁ ▁and ▁formed ▁cr aters ▁ ▁west ▁of ▁The ▁Ch ord , ▁giving ▁observation ▁over ▁the ▁objective . ▁ ▁The ▁new ▁cr aters , ▁A , ▁B ▁and ▁C , ▁older ▁cr aters ▁ ▁Tri angle ▁Cr ater ▁were ▁occupied ▁and ▁the ▁ 1 7 0 th ▁T unn elling ▁Company ▁destroyed ▁German ▁mine ▁ent ran ces ▁found ▁in ▁the ▁Tri angle ▁Cr ater . ▁German ▁counter - att acks ▁re to ok ▁Tri angle ▁Cr ater ▁on ▁ 4 ▁March ▁and ▁from ▁ ▁sk irm ishing ▁took ▁place ▁during ▁heavy ▁snow st orm s ▁and ▁bitter ▁cold . ▁German ▁attacks ▁dimin ished ▁until ▁ 1 8 ▁March , ▁when ▁five ▁mines ▁were ▁blow n , ▁the ▁captured ▁port ions ▁of ▁The ▁Ch ord ▁were ▁re - t aken ▁and ▁the ▁British ▁were ▁driven ▁back ▁to ▁the ▁old ▁front ▁line . ▁The ▁Germ ans ▁found ▁the ▁area ▁equally ▁un ten able ▁and ▁retired ▁to ▁the ▁eastern ▁side ▁of ▁the ▁cr ater ▁lips . ▁The ▁British ▁had ▁found ▁the ▁cr aters ▁to ▁be ▁poor ▁protection ▁against ▁bomb ard ment ▁and ▁the ▁mor ass