In war, absolute secrecy is essential to the success of any invention, and the British engineers were determined to let no inkling of the new armored automobiles reach the enemy. Different parts of the machines were made in different factories, so that no one would have an idea of what the whole would look like. At first the new machine was known as a "land-cruiser" or "land-ship"; but it was feared that this very name would give a clue to spies, and so any descriptive name was forbidden. Many of the parts consisted of rolled steel plates which might readily be used in building up vessels to hold water or gasolene; and to give the impression that such vessels were being constructed the name "tank" was adopted. The necessity of guarding even the name of the machines was shown later, when rumors leaked out that the tanks were being built to carry water over the desert regions of Mesopotamia and Egypt. Another curious rumor was that the machines were snow-plows for use in Russia. To give some semblance of truth to this story, the parts were carefully labeled, "For Petrograd." Probably never was a military secret so well guarded as this one, and when, on September 15, 1916, the waddling steel tractors loomed up out of the morning mists, the German fighters were taken completely by surprise. Two days before, their airmen had noticed some peculiar machines which they supposed were armored automobiles. They had no idea, however, that such formidable monsters were about to descend upon them. The tanks proceeded leisurely over the shell-torn regions of No Man's Land, wallowing down into shell-holes and clambering up out of them with perfect ease. They straddled the trenches and paused to pour down them streams of machine-gun bullets. Wire entanglements were nothing to them; under their weight steel wire snapped like thread. The big brutes marched up and down the lines of wire, treading them down into the ground and clearing the way for the infantry. Even trees were no barrier to these tanks. Of course they did not attack large ones, but the smallish trees were simply broken down before their onslaughts. As for concrete emplacements for machine-guns, the tanks merely rode over them and crushed them. Those who attempted to defend themselves in the ruins of buildings found that the tanks could plow right through walls and bring them down in a shower of bricks and stone. There was no stopping these monsters, and the Germans fled in consternation before them.