In his war memoirs, "Storm of Steel" Ernst Junger remarks on seeing a German soldier in a steel helmet for the first time in August 1916, during part of the Some battle.
The reason for the slow introduction of the Brodie helmet to British and Imperial troops is a little more involved than has been represented here, I believe. I was told that there were manufacturing problems with the Brodie due to it being produced by "punching" the shape into a single sheet of steel. Unless you are very careful, what happens is that the deeper the pressing, the more the steel is stretched and the thinner it becomes - usually at the place you want it to be at its strongest, namely the top of the crown. It took some time for many of the companies manufacturing the helmet to sort this out, during which time helmets had been issued to some units. Haig and his staff decided to remove the helmets from these units and re-issue them as "trench stores" so that anyone serving in the front line had a helmet. Eventually the problem was solved (the Germans apparently sorted it out almost immediately) and enetually helmets were issued to every individual in France, but it did lead to another "Haig-hater myth" that he had stopped his men wearing helmets because it "destroyed their offensive spirit".