Mustard gas (or Yellow Cross, as it was called officially by the Germans) was the war gas par excellence for the purpose of causing casualties. Indeed, it produced nearly eight times more Allied casualties than all the various other kinds of German gas. It was used for preparation a considerable time before the attack, or during the attack, on localities and objects with which the attackers would have no contact.
Blue Cross.—Another new type, the German Blue Cross, was introduced about the same time. This represented at different times diphenylchlorarsine, diphenylcyanarsine and other arsenic compounds. The Blue Cross compound was contained in a shell with high explosive. The enemy expected that the shell burst would create such a fine diffusion of the compound that it would penetrate our respirator mechanically, and then exercise its effects. These, violent irritation of the nose and throat, nausea and intense pain, would cause the removal of the respirator and allow other lethal gases to have full play. Fortunately, the German hopes of penetration were not realised, but they were, no doubt, continuing to develop the vast possibilities of the new method.
German Emphasis on Gas Shell.—The Green Cross or lethal filling was another type of German gas shell. Green Cross covered such compounds as phosgene and chlor-methyl chloroformate. Although these caused fewer casualties than mustard gas, they were relatively more fatal. Schwarte's book tells us that, "After the introduction of the Green Cross shell in the summer of 1916, at Verdun over 100,000 gas shell were used to a single bombardment."
From the time of the first use of mustard gas until the terrific gas shell attack of March, 1918, the Germans persistently used their new types against us with considerable effect. Even when the period of surprise effect with mustard gas was over, the number of casualties caused by it was considerably greater than during the months when the Germans were firing only non-persistent lethal shell of the Green Cross type. The Germans regarded these shell gas developments as largely responsible for our failure to break through in the Autumn of 1917.
The German Projector.—During this period they also developed a projector. Their first use of it was again co-ordinated with an attempt at surprise. Fortunately, protection and gas discipline had reached such an efficient state that normal "alert" conditions of the front line system were largely able to counter the use of this new device by Germany. The first attack was against the French at Rechicourt on the night of December 5th-6th.
On the night of December 10th-11th, 1917, they fired several hundred projectiles on the Cambrai and Givenchy sectors of the British line. In both cases the gas bombs were fired almost simultaneously into a small area including our front and support lines. The bombs appeared to have been fired from the enemy support line, as observers state that they saw a sheet of flame run along this line, followed by a loud explosion. The bombs, which emitted a trail of sparks, were seen in the air in large numbers and made a loud whirring noise. They burst with a large detonation, producing a thick, white cloud. The discharge was followed immediately by a bombardment with H.E. shrapnel and gas shell, and a raid was attempted south of Givenchy. We learn that so strong was the gas discipline that in many cases respirators were adjusted before the arrival of the bombs, the resemblance to our projector attacks having been established at once. When this was done practically no casualties occurred. Again, to show the efficiency of British protection against projector gas, we learn from official reports that, "At one point five bombs burst in a trench without harming the occupants. It should be remembered that the British box respirator protects against very high concentrations of gas which pass at once through the German mask." Similar discharges were made against the French on two occasions in December, and against the Lens sector on December 30th. The compounds used in the bombs were phosgene and a mixture of phosgene and chlorpicrin. These attacks increased in number during the ensuing months.
German Projector Improvements.—The Germans developed a longer range modification and would undoubtedly have exploited this weapon very considerably but for the trend of the campaign. The Allied advance in 1918 uncovered a number of enemy dumps. Amongst the most interesting was one which contained a number of a new type of projector.
A prisoner of the 37th pioneer gas battalion, captured on August 26th, had said that they were to practise with a new type of projector with a range of 3 kilometres, the increased range being obtained by rifling the bore of the projector. He stated that the intention was to use the longer range weapons in conjunction with the old short range projector, using the new type to deal with the reserve positions. The capture of the dumps referred to above revealed the truth of his statement. Two kinds of bombs were used, one containing H.E. and the other small pumice granules impregnated with phosgene. This was an ingenious attempt to produce a persistent but highly lethal gas by physical means, for hitherto the highly lethal gases had only been slightly persistent. The new projector had a calibre of 158 mm. and was termed the "Gaswerfer, 1918." The importance of this new projector cannot be overestimated. Its large scale use would, undoubtedly, have resulted in imposing stringent gas alert conditions at greater distances from the front line.
Dyes in Gas Shell.—Another interesting German development of this period was the use of certain dyes or stains in gas shell. After gas bombardments in the winter of 1916-17, the snow was seen to be covered with coloured patches. These coincided with the bursts of the shell. Analysis of the earth showed that the colour was due to the presence of an actual dyestuff. A number of explanations were advanced to account for the use of the colour, of which the most probable claimed its employment for the identification of affected localities several hours or even days after the bombardment. This was especially the case with persistent types. As the explosive charge of chemical shell was feeble, some such means of identification was necessary. It may be that the Germans expected that troops advancing after such bombardments would be helped by the splashes of colour, and that these earlier attempts were purely experimental.
German Flame Projectors.—We have already referred to the use of flame projectors by the enemy, and a picturesque account of their development and use in the later stages of the campaign is found in an extract from the Hamburger Nachrichten of the 9th of June, 1918: