This process plainly was a very delicate one, even in its beginning. It seemed a little nervy to order soldiers to advance while above their heads hissed and barked their own gunners' shells. Sometimes these would burst before they got to the curtain line and casualties would inevitably result. It was rather ticklish business for the men to charge forward even if they were a couple of hundred yards behind such a hail of steel. Soon, however, another improvement was put into effect and that was to shorten the barrage to sixty yards, letting the soldiers advance with the exploding shells nearer and nearer to their own bodies. Of course, there was great advantage in this, as the closer the troops were to the curtain fire ahead, the better they were protected and the shorter was the time after the curtain was lifted until the troops occupied the trench. Cutting this time down to the minimum made it so much harder for the Germans to emerge from their hiding and resist the oncoming troops. The science of this was at last so well worked out that a gap of less than forty yards lay between the curtain and the troops and sometimes only thirty yards which could be covered in a couple of seconds after the barrage was lifted. Time, of course, is the chief element in the endeavor to get the bulge on the other fellow. Finally the British worked out what they call the "creeping barrage." This takes into account the fact that the trenches are never exactly straight and parallel. But here the camera came to the aid of the Allies and it told them just how much deviation from the parallel there was. From these photographs the relative positions of the trenches at any given point were plotted out accurately, showing the irregular shape of No Man's Land and the variation of its width at all the different places. The Allies then dug identical trenches in the rear and practiced on them. This changed the method of curtain fire from "regular" to "creeping." From that time the barrage started in a line which first followed the shape of our own fire trench, but as it moved forward the configuration was altered and it swayed and wriggled like a snake gradually taking the shape of the enemy's trench. Plainly, it required much deeper skill to employ this method, but its advantages were great. Instead of all the gunners shooting in unison at a single command, each one had a different job to perform in order to make the barrage conform with the angle which the trenches made. This is now the general method and has been brought up to a marvelous degree of accuracy as well as speed.