OPENING LINE • DICTIONARY ONE.COM • Definition of Opening line

... Company of nine Tanks were to co-operate with the Brigade, advancing immediately behind the first line. The attack was to be launched at dawn and was to be carried out under an artillery barrage which, after delaying six minutes on the opening line, was to move at the rate of 100 yards in four minutes. The delay was to enable the Infantry to adjust their distance behind the barrage, which was to open a good deal further in front of them than usual, owing to the fact ...

— The Sherwood Foresters in the Great War 1914 - 1919 - History of the 1/8th Battalion • W.C.C. Weetman