From Hundred Days: The Campaign That Ended World War I, by Nick Lloyd (Basic Books, 2014), Kindle Loc. 2110-2134, 2146-2157:
Following up the German armies was never easy or without cost. As well as advancing in the face of shelling, booby-traps, and machine-gun and sniper fire, the Allied armies had to operate in a terrifying and dangerous chemical environment. Although shell and machine-gun fire accounted for the majority of casualties, gas evoked a fear that was unlike any other weapon and had a significant effect on how the war was fought. It had evolved much since the first chlorine gas had been released near Ypres in 1915, maturing into a weapon that was used with a remarkable degree of ingenuity and inventiveness. By 1918 all sides had incorporated gas into their battle tactics, with both front and rear sectors regularly being deluged with gas, which poisoned the ground and caused a constant trickle of casualties. Gas shells, containing either mustard or phosgene, would often be fired alongside high explosive, in the hope that during a bombardment – with its noise and chaos – the arrival of quieter gas shells would be missed. If any soldiers survived the bombardment, then a silent, deadly killer would still await them. Gas also offered a useful and effective method of counter-battery fire. Because it was very difficult to score a direct hit on enemy gun positions, gas shells were frequently employed to force gunners to don their respirators, which often impeded their accuracy and slowed their reactions.
For the Allies, the main problem was dealing with mustard gas – ‘the king of the war gases’ – which was used in increasing amounts by German artillery. As the retreat gathered momentum, German gunners fired thousands of these shells at their pursuers, using it as an area denial weapon, through which the Allies could not advance, or at least not without difficulty. As the historian Tim Cook has shown, ‘German gunners simply blocked out map grids and fired shells to saturate the whole sector, thereby eliminating that area from the front.’ Ever since its introduction in the summer of 1917, mustard gas had become notorious for its effectiveness at causing casualties because of its persistence and the lack of a foolproof countermeasure. The German chemical industry produced vast amounts of this effective and unpleasant chemical compound, while the Allies could only manufacture limited amounts by the summer of 1918. Mustard gas may not have been immediately fatal (particularly if there was only minor contact), but it caused a variety of painful wounds, including lung damage (if inhaled), blisters and burns on the skin, and conjunctivitis in the eyes. The shells would explode with a dull thud or pop, leading some inexperienced soldiers to mistake its arrival for that of a ‘dud’ shell. The liquid contents would then leak out, rapidly vaporize and form terrifying yellow clouds. Because it could go through wool and cotton, there was precious little protection from its symptoms, particularly if the liquid splashed you, and it lay there, settling in shell holes and trenches, often remaining active for weeks. It is little wonder that unless dealt with quickly the fear of mustard gas had a devastating effect on unit morale. All soldiers could do was put on their gas masks and try to get out of the affected area as soon as possible. Unfortunately, this was sometimes easier said than done because German gunners had an annoying habit of creeping their gas barrages forward at the same rate as a man could walk. If you were particularly unfortunate, you could be exposed for hours.
The Americans – who began their own offensive in September – would also encounter the horror of mustard gas. Indeed, Pershing’s forces were particularly susceptible to gas attacks as they lacked the sophisticated and well-worn anti-gas doctrine of the British and French. Whereas the Allies had been gradually improving their protective measures since 1915 (and were well aware of how deadly chemical weapons could be), there was a lack of appreciation in the US Army of how easily gas could cause casualties. Gas accounted for 27 per cent of American losses in the Great War, a frighteningly high figure that, in part, explained the speed with which large US divisions were worn out at the front.17 One American officer, Frank Holden, a Battalion Gas Officer, experienced a gas bombardment that September. It was a terrifying few hours that revealed not only how inventive gas tactics were becoming, but also how difficult they were to combat. Holden knew that the Germans often fired tear gas (or what was known as Blue Cross gas) into areas where troops had concentrated, causing intense choking, sneezing and coughing. After Blue Cross had been deployed, German gunners would then deluge the target area with more deadly agents, many men often finding it impossible to keep their respirators on if they needed to sneeze or vomit. Holden’s battalion had marched into the village of Norroy when they came under a barrage of ‘sneezing gas’ (most probably Blue Cross). He immediately ordered all gas masks to be worn.