[1] Journal of the Royal Artillery, February, 1920.

Fixed Gas Barrage at Kemmel.—Another most interesting example is also quoted, dealing with the shelling preceding the attack on Kemmel on 25th April. "This is an interesting case, as non-persistent Blue Cross shell were used within the objective and Yellow Cross just behind it, indicating that on 25th April the enemy did not intend to go beyond the line they gained."

Percentage of Chemical Shell.—Some idea of the importance which the Germans attached to their chemical ammunition, as distinct from explosives, can be gathered from the following extract from a captured order of the Seventh German Army, dated May 8th, 1918, giving the proportion of chemical shell to be used in the artillery preparation for the attack on the Aisne on 27th May, 1918.

"(a) Counter-battery and long range bombardments.
For 7.7 c/m field guns, 10.5 c/m and 15 c/m,
howitzers and 10 c/m guns; Blue Cross 70%,
Green Cross, 10%; H.E. 20%, long 15
c/m guns fire only H.E.
(b) Bombardment of infantry positions.
(i) Creeping Barrage.
For 7.7 c/m field guns, 10.5 c/m and 15
c/m howitzers; Blue Cross 30%, Green
Cross 10%, H.E. 60%, 21 c/m howitzers
fire only H.E.
(ii) Box Barrage.
For 7.7 c/m field guns, 10.5 c/m howitzers
and 10 c/m guns; Blue Cross 60%, Green
Cross 10%, H.E. 30%."

What more striking demonstration is needed than these extraordinarily high percentages?

Gas Retreat Tactics;—General Hartley's Analysis.—No Yellow Cross shell were to be used in the bombardment, but, as mentioned above, there was a complete change of tactics in their retreat, during which they attempted to create a series of barriers by literally flooding areas with mustard gas. This defensive use of mustard gas was most important. Again, quoting General Hartley, "Yellow Cross shell were used much farther forward than previously, bombardments of the front line system and of forward posts were frequent, and possible assembly positions were also shelled with this gas. On more than one occasion when an attack was expected the enemy attempted to create an impassable zone in front of our forward positions by means of mustard gas. Their gas bombardments usually occurred on fronts where they had reason to fear an attack, with the idea of inflicting casualties in areas where troops might be massing. It was instructive to note how supplies of Yellow Cross shell were switched from the Third to the First Army front late in August when they became nervous about the latter sector. In Yellow Cross they had an extremely fine defensive weapon, which they did not use to the best advantage, for instance, they neglected its use on roads and did not hamper our communications nearly as much as they might have done. As our offensive progressed their gas shelling became less organised, and one saw very clearly the superior value of a big gas bombardment as compared with a number of small ones. In the latter case it was usually possible to evacuate the contaminated ground and take up alternative positions, while in the case of a bombardment of a large area such as the Cambrai salient, the difficulty of doing so was greatly increased, and consequently casualties were higher. During our offensive it was not possible to exercise the same precautions against gas as during stationary warfare, and the casualties were increased on this account."

Percentage of German Gas Shell in Enemy Dumps.—A test of the importance attached by any army to the different types of ammunition which it uses can be made by examining the percentage of such types of shell in a number of ammunition dumps assembled behind the front line for some specific operation, or part of a campaign. An examination of German production from this point of view is very interesting, and also brings out a significant point. The normal establishment of a German divisional ammunition dump in July, 1918, contained about 50 per cent. of gas shell. The dumps captured later in the year contained from 30 per cent. to 40 per cent. These figures are significant, for they show how much importance the German Army attached to gas shell. When we think of the millions of shell and of the huge quantities of explosives turned out by our own factories to fill them, and when we realise that for a large number of gun calibres the Germans used as many shell filled with gas as with explosive, some idea of the importance of gas in the recent war and of its future possibilities can be obtained. Further, when we realise that the production of explosives can be controlled and inspected during peace, but that no such control can exist for chemical warfare products, the significance for the future stands revealed.

Forced Exhaustion of Stocks.—It might be thought that the lower percentages found later on in the year were an indication of the decreasing importance of chemical shell. Examining the case less superficially, however, we soon see that this lower percentage has an entirely different meaning. In the first place, we know that the German factories were still pressing on to their maximum output at the time of the Armistice. New units were being brought into operation. Secondly, we have seen how huge quantities of mustard gas were diverted to those particular German armies which were most threatened by the final Allied offensive, indicating that certain portions of the German front were being starved for chemical shell. The truth of the matter is that the Germans had accumulated enormous stocks for their great offensive and that they had expended these stocks at a greater rate than their factories could replace them. We learn from Schwarte's book that, "Although the production of Yellow Cross almost reached 1000 tons a month, yet finally the possibilities of use and the amount required were so great that only a much increased monthly output would have been sufficient."

Yperite, French Mustard Gas.—During this period the volume of allied gas activities also increased considerably. But until June, 1918, our success was due to the development of more successful tactical methods rather than to any specific chemical surprise.

Very great credit is due to the French for having produced large quantities of mustard gas by the above date.