Before proceeding any further it will be as well to discuss briefly the cause of this disaster. In the first place, this was only the second concentrated bombardment with mustard gas that had occurred. The first had taken place at Ypres a month before, and caused extensive casualties, but the report of these did not reach us till the night of relief, when it came with the usual correspondence, which, owing to pressure of work, was not opened till after the disaster had happened. The significance of the new form of gas should certainly have been circulated earlier. With the dangers of ordinary gas we were familiar, and in any case no one could have lived for five minutes in the area most strongly affected without a respirator. The slightest breath of this new gas was like inhaling red-hot air and choked you immediately. After the first density of the gas had dispersed, the area became comparatively clear, and the insidious and silent evaporation, practically free from smell, caused no one inconvenience, and in some places was so slight as to be barely perceptible. It was this that affected the eyes, an entirely new phenomenon to us; and the comparatively small number that suffered from serious internal gassing proves that the ordinary precautions were taken. Moreover, most of those badly gassed were actually caught in Armentières itself by the original barrage, which began at the rate of hundreds of shells in a minute. When it is remembered that as late as the spring of 1918, after mustard gas had long been recognized and widely advertised, and every possible precaution taken against it, a concentrated bombardment still produced casualties running into hundreds, it is not so very surprising that on the second occasion when it was used, and the first as far as we were concerned, only about fifty escaped out of the total troops in Armentières, consisting of two half battalions, some field and heavy batteries, and some Royal Engineer, Machine Gun Corps, and Trench Mortar sections. Of the civilian population, it is probable that scarcely one single person got off unscathed.