The actual gas wave was accompanied by a heavy bombardment of the front line and of Ypres and the villages behind it, shrapnel and high-explosive shell and also tear shell being used, the latter shell being fired particularly against our artillery. This bombardment lasted throughout the day and most of the following night. Though our wire had been cut in many places by the artillery fire, the Germans made no serious infantry attack, and small patrols which left their trenches in a few places were immediately shot down, as our fellows were continually on the alert and had not suffered to any considerable degree. Altogether a large number of troops were exposed to the gas, but, compared with its extent, the cloud caused only a small number of casualties. This was very satisfactory after our experiences of the spring. Men who were gassed but not killed were all subsequently questioned as to the reason for their being gassed, and in each case a definite reason was forthcoming. In no single instance was the fault laid at the door of the smoke helmet, which apparently had been quite capable of standing up to the highest concentrations in any part of the cloud. Among the reasons given for the casualties were things like the following: Some men in the fire trenches did not get on their helmets quickly enough owing to the short distance between the trenches, lack of warning in the support line and insufficient practice. Some officers and men sleeping in dugouts did not have their helmets attached to them or they were caught away from their dugouts without helmets. Helmets in many cases were under the overcoats, which made it very difficult to get them and put them on quickly, as it was necessary to undo the overcoat, the top button of the jacket and the cardigan waistcoat before the helmet could be tucked in. One cause of casualties was that the “P” helmet smelt very strongly of carbolic, and a lot of men who had not had this explained to them thought that the peculiar smell was that of gas coming in and they took their helmets off with a view to replacing them with other helmets. This of course was fatal. One sergeant was gassed through his helmet’s being holed by a bullet, though he himself was not wounded. In some cases wounded men tried to remove their helmets and were gassed in this way, and it was found necessary to watch men who were hit to prevent this. In many ways this attack of the Germans was of the greatest importance, as it displayed all of the features on which the subsequent development of the gas cloud was based. These features were: Increased concentration; the use of new material; surprise. These three things are really the basis of all gas warfare, even at the present day, whether the attacks are made in the form of clouds or by the use of gas shells or other projectiles.