In the seven months since the German Army first tried chlorine gas against them at Ypres, the British Army has manufactured and distributed hundreds of thousands of  ‘P helmets’ (actually hoods treated with sodium phenate) like the ones seen above being worn by a Vickers gun crew. This production achievement has successfully hardened the British soldier against chlorine, a weaponized waste product of the German chemical industry, and so Dr. Fritz Haber has prepared a new experiment with phosgene gas today.

For three weeks, a specialized unit — Pioneer Regiment 36 of the 52nd Reserve Division — handled and emplaced hundreds of canisters to release thousands of pounds of an 80:20 mixture of chlorine and phosgene; as usual, Haber personally inspects their work. Ever the scientist, today’s operations plan — developed by 4th Army, yet personally approved and modified by Haber among many hands — targets the flanking elements of the 49th Division with tear gas and high explosives to mitigate the intervening variable of enemy action. Only lately given a formal office within the German military-industrial complex, Haber has developed chemical shells to target enemy formations with precision; they are also used today, but production bottlenecks are still preventing their deployment in mass numbers just yet.

The attack plan today is hardly a full-scale assault on the British line at Wieltje, the devastated former site of a small Belgian town north of Ypres. Instead, specialized squads equipped for trench fighting on a chemical battlefield will set out to follow the great cloud in raiding formations to discover the effects of the gas. The 4th Army wants to know whether present gas technology can provide a mass breakthrough, but they are not mounting a major offensive in order to observe the results.

German trench raiders training in the Argonne during late 1915. Note the experimental goede helmets

More persistent than chlorine alone, phosgene lingers in low points like a deadly ghost for up to 48 hours, and sometimes kills its victims a full day after exposure. Insidious, phosgene causes less choking than chlorine, and is therefore more fully inhaled by the victim. It has been used on Russian troops already, so British intelligence was quite aware of its existence as a weapon, but a more specific coup has allowed the British Army to prepare for today’s assault in advance — and unlike the first British experience with a gas attack at Ypres, this time the command chain has responded to warnings with alacrity.

Like every unit in the British line, VI Corps has developed its own trench raiding forces, and two weeks ago one of these squads captured a senior German noncommissioned officer who revealed the pending attack. Since May, the entire British line has developed a system of weather and wind monitoring stations to give advance warning of favorable conditions for a gas attack all along their line; the meteorology stations on the front of VI Corps have increased their reporting frequency as those conditions improved in recent days. With shell and gun production still at a premium, small howitzers are brought in to try detonating the cylinders in the German front line trenches, but the firepower is insufficient. Troops are kept in a state of readiness, often wearing their P-helmets while on watch, or rolled on top of their heads with the top button of their greatcoats open so they can quickly be rolled down and secured. Gongs and horns have been positioned throughout the sector to alert troops as soon as the deadly cloud is sighted.

A parachute flare announces the operation with standard German punctuality at 5 AM. Shortly thereafter, a fifty-foot high cloud of greenish gas forms across a mile-long front, blowing up to ten miles inland, killing some sleeping troops in reserve trenches and billets who are still not warned in time, despite all their defensive preparations. But the P helmets are proof against the gas as long as they are donned immediately. Of more than a thousand gas casualties sustained today, only about ten percent are killed, and so the German scouting parties meet a stiff resistance from accurate British rifle fire from the moment they cross their parapets. The lethal cloud is blown clear after a half-hour; a desultory rain of chemical shells continues for ninety minutes, but with little effect.

As a result of the experiment, the German Army concludes that gas alone cannot achieve a breakthrough in trench warfare. During January, new British P helmets are treated with hexamine to improve their performance against phosgene; the superseding new design is designated as a ‘PH helmet’ while new respirator models are developed to answer German ones. Having begun as a war of generals, the Great War is turning into a violent clash of scientists and engineers.

A famous photo of German trench life taken near Wieltje. The newspaper is evidence of successful raiding on the British line