The second attack was one of the most interesting on record, for it was here, near Hulluch, that the gas blew back on the Germans and killed many more of them than our total gas casualties. The thing happened in this way: The first gas wave was loosed off at three-fifty A. M., opposite the celebrated Chalk Pit Wood. Fifteen minutes later a heavy cloud was discharged on the Hulluch front. But the wind was too light and variable. The cloud came over our line and then the gentle wind first dropped altogether and then gradually veered round. The gas hung on No Man’s Land and over both sets of trenches for a short time, and then with increasing pace drifted back right over the German position, just where Fritz had been seen massing for an attack on the Hulluch sector. We did not see the confusion which reigned, but almost simultaneously with the arrival of his own gas our barrage came down and the German attack dispersed. All that day our observers reported the carrying out of German casualties from the trenches on stretchers and a constant stream of ambulances coming up and then returning along the roads to the rear. We surmised that the boche had swallowed some of his own poison, but it was not until several months later, from some documents captured during the Battle of the Somme, that we were able to appreciate his disaster to the full. The first of these documents was the diary of a soldier who had been in the neighbouring trenches. It ran: “... We went along the trenches to find the headquarters of the ----th. It was awful. Everywhere lay dead bodies or men gasping for breath and dying from the gas. Somebody must be to blame. At first I could not go on. One almost had to step on them to get through. I asked an officer of the ----th what had happened. They were going to be relieved....”