The French did not try to hide the roads, but they concealed the traffic on the roads by hanging rows of curtains over them. As these curtains hung vertically and were spaced apart, one would suppose that they would furnish little concealment, but they prevented an observer in an aëroplane from looking down the length of a road. All the road he could see was that which lay directly under his machine, because there he could look between the curtains; if he looked obliquely at the road, the curtains would appear to overlap one another and would conceal operations going on under them.
In one case, the Germans completely covered a sunken road with canvas painted to represent a road surface. Under this canvas canopy, troops were moved to an important strategic point without the slightest indication of such a movement.
Nature's tricks of camouflage were freely used in the hiding of the implements of war on land. Our big guns were concealed by being painted with leopard spots and tiger stripes, the color and nature of the camouflage depending upon the station they were to occupy. In many cases, they were covered with branches of trees or with rope netting overspread with leaves. So careful was the observation of the air scouts that even the grass scorched by the fire of the gun had to be covered with green canvas to prevent betrayal of the position of the gun.
In the making of an emplacement for a gun it was of the utmost importance that no fresh upturned earth be disclosed to the aërial observers. Even foot-paths leading to it had to be concealed. Plans were carefully made to cover up all traces of the work before the work was begun. Where it was impossible to conceal the paths, they were purposely made to lead well beyond the point where the emplacement was building, and, still further to deceive the enemy, a show of work was sometimes undertaken at the end of the path. Wherever the sod had to be upturned, it was covered over with green canvas. The earth that was removed had to be concealed somewhere and the best place of concealment was found to be some old shell-hole which would hold a great deal of earth without any evidence that would be apparent to an observer in an aëroplane. If no shell-hole were handy, the excavated material had to be hauled for miles before a safe dumping-ground could be found. As far as possible everything was sunk below the earth level. Big pits were dug in which the mortars were placed, or if a shell-hole were empty, this was used instead.