Another great danger in winds of too low velocity is that these are just the winds which change their direction most frequently, and anything under two miles per hour is just as likely to blow the gas back to the place from which it came. It was disregarding this principle on one occasion later on that caused the Germans numerous casualties from one of their own gas clouds. In general, however, it may be laid down that the most favourable winds are those between four and twelve miles an hour, so that with a wind of eight miles an hour the cloud would move just twice as quickly as a man walking rapidly, and would take only twelve and a half seconds to cross No Man’s Land in places where the trenches are fifty yards apart. Let me try to give an account of the procedure of carrying out gas attacks as it was told me by a German prisoner taken not so very long ago. He said: “I am not one of the gas pioneers, but being an engineer by trade and having been in the trenches for many weeks with the 35th Regiment of Pioneers I have got to know their methods fairly well. Indeed I assisted on one occasion in carrying cylinders into the trenches for an attack against the British. Gas is not popular with us; we have had too many mishaps, and the cylinders are a nuisance to carry into the trenches. They weigh ninety pounds and they are always carried in by the infantry. A gas regiment does not do that for itself. It is a long carry and it is really more than a one-man load. At the most two men are allotted to carry in each cylinder, whatever the distance. “Several thousand of these cylinders must be taken into the trenches, and then we have the job of putting them in position. Deep holes are dug just underneath the parapet of the trench, and into these holes are placed the separate cylinders with the tops flush with the ground. As each cylinder is placed into position the hole is covered with a board, on top of which is placed a thing we call a ‘_Salzdecke_,’ which is really a kind of quilt stuffed with peat moss and soaked in potash solution so as to absorb any of the gases that may leak out. “On top of the _Salzdecke_ are built up three layers of sandbags, so that there is not much danger of the cylinders’ being hit by shell fragments. This also serves to hide the cylinders in case a raid is made, and the sandbags form an excellent firing step. In fact, you would never guess that the gas was ready in position to make an attack. All of this takes a long time to do, and then we have to wait for a wind that is favourable.