 Moving troops to the front ahead of the attack was still extremely difficult, as the only means of approaching the front line were narrow boardwalks made of planks, which wound between the shell-holes.Slipping off duckboards could often be deadly with unfortunate soldiers frequently drowning in mud under the weight of their equipment.Because of the exhausting nature of the journey, the leading assault units entered the support line four days before the battle to ensure that the soldiers would be as fresh as possible for the attack.