Summer of 1916 the highwater mark of the German gas cloud--Their improved methods--The need of speed and secrecy--Gas as a rat exterminator--Causes of Allied casualties--Germans killed with their own gas--Gas masks for horses and mules--Reduced Allied casualties--Humorous incidents. The great time for the German gas troops was undoubtedly 1916, and from April to August of that year they carried out five big cloud gas attacks on the British alone, not counting several on the French Front and a number against the Russians. During the interval from the December attack of the previous year they had obviously been thinking hard and preparing lots of gas, for the new attacks showed several fresh features both as regards extent and tactics. Along the lines of making the gas more poisonous, using greater quantities and higher concentration and the springing of surprises, everything was done to make the gas cloud an even more deadly affair than it had been in previous shows. That our own casualties were much less than before, and that the boche in at least one case had a lot more killed by his own gas than we had, were very satisfactory results of all the labour and research as far as we were concerned. For the same reason that the December attack had been reduced in duration to half an hour, the new clouds lasted only ten to fifteen minutes; thus once more multiplying the concentration by two or three. On top of this the amount of phosgene was increased up to at least twenty-five per cent and probably to about fifty per cent, so that in this way also the cloud became much more deadly than before. It is interesting to note that pure phosgene cannot be used, otherwise the Germans would undoubtedly have employed it. Straight phosgene does not come out of the cylinders satisfactorily--it must have a big proportion of something like chlorine mixed with it to force it out and get it into the air as quickly as may be. All of this made the gas cloud a nasty thing to face. As it became progressively more deadly it required less and less to kill. A couple of breaths of the poisoned air became enough to kill a man; but as our protection was good enough, it meant that the most important thing for the enemy to do was to take us unawares by getting his gas over so quickly or deceiving us in some other way that we should be down and out almost before we knew it. This is where his surprise tactics came in. These tactics consisted in attempting a great secrecy in the preparations, in the use of smoke clouds to put us off the real track of the gas, and the putting over of a number of different waves of gas at varying intervals. The value of the last two will be more apparent from the accounts of the individual attacks, but the importance of the first-mentioned method must be emphasised a bit.