My memory may fail me, but I'm sure I read in Corrigan that the infamous "walk order" is a myth? From what I recall, it came from over-cautious army commanders who were concerned about their battalions getting separated, but was generally disregarded by battalion commanders. Some did walk, but others ran, some crawled into No Man's Land before the barrage lifted so they could rapidly rush the parapet, and still others dug Russian saps to get them closer to the Germans.

What is true is that the BEF of 1916 was too low quality to execute the kind of fire and movement tactics it had in 1914, and the French had developed in the bloody crucible of Verdun. While these sorts of tactics meant it could take the French hours to cross No Man's Land, combined with a considerably greater number of guns in their sector, they allowed the French to gain every single one of their first-day objectives. To make a depressing contrast, only the British XIII Corps achieved its objectives on the First Day, and success was not exploited.