I don't do much reading with regards to WW1, but I may indulge after seeing a few newer WW1 docs and TV specials on the subject. Recently I have been watching a few on Vimy and what Aardy is saying was covered in them. I will add a few other things that I didn't know that came out in the shows. The battle plan was meticulous, with 3D planning with the use of maps and a scaled mock up being used as well. They also broke down the tactics to a unit level, with the companies actually being in on the battle plan, being given maps to use as well. They taught the companies how to keep up with the creeping barrage, so that they would be on top of the enemy positions before they knew it. Mop up troops were also introduced, who would keep behind the main advance because the Germans were known to pop up after the advance, making the advance bog down because of their presence. Whether or not underground refuges were used the way they were at Vimy I do not know, but it would seem that many underground refuges, they were called "subways" were carved out, so that troops could remain safe from shell fire, but be near the front line trenches, ready to go into battle. These "subways" could hold hundreds and with many of them probably thousands of troops.