>So you were really only left with a creeping barrage or a mass formation running to the other line.

I was going to make a technical and slightly pedantic point, but I've realised it might be one that illustrates something important about WW1 that /u/Version2dnb might be interested in.

What is a creeping barrage? A creeping barrage is an artillery barrage that moves forwards at a slow, steady pace (typically in 50-100 yard increments). If your opponents are sitting in some trenches, why not just keep hitting those trenches rather than moving your barrage?

A creeping barrage has three main goals: to keep the enemy's heads down while your own advance, to prevent reinforcements advancing or defenders retreating, and to throw up smoke and dust to cover the advance.

It "creeps" forwards so that it stays ahead of your own troops as they advance. There's no need to communicate with the artillery to say "we've reached this line, move the barrage", something that was difficult to do in the early days of field telephones. The troops just have to stick to the timetable of the barrage.

Of course, "just stick to the timetable" is anything but easy. But the whole idea shows how armies were trying to figure out ways to use combined arms and to deal with the problems they faced on the battlefield. Techniques for barrages became increasingly complex and effective as the war went on.