After successfully holding the Germans back at Ypres the allied commander, Frenchman Field Marshal J.J.C. Joffre, developed a new plan for breaking through the German lines in three different places; Artois, the Champagne Valley, and Loos. The Loos offensive would be left up to the British First Army (including the Second Battalion Border Regiment) commanded by General Douglas Haig.
At first General Haig, concerned with the poor condition of his army after Ypres and a shortage of artillery shells, tried to postpone the attack, but intense pressure from Field Marshal Joffre caused him to go ahead. In addition to artillery, General Haig was allowed the use of chorine gas to offset the shortage of artillery shells, and Loos became the first battle in which the British would use poison gas.
The attack began on the 25th of September with the release of 5,243 British gas cylinders. 600 Germans were killed outright in the gas attack, and the British forces pushed forward almost 4,000 yards. Then the battle turned ugly for the British.
Much of the gas was caught in the wind and blown back on the British infantry as it advanced. The British artillery began its barrage on the German lines but had little effect in knocking out the German trenches and emplacements. Subsequently the German machine guns, who knew full well which direction the infantry attack was coming from caught the advancing British in a deadly crossfire. In the smoke and clouds of gas, the British could not tell where the machine guns emplacements were, and they stumbled blindly about, all the while getting shot to pieces. Entire battalions were all but wiped out in a matter of minutes.
The British assaults continued with similar results for several more days. Until, by the 28th, the fighting at Loos had ended. In another week, by the 8th of October, the Third Battle of Artois and Second Battle of Champagne had also ended with similar disastrous results for the allies. The British forces alone had suffered 60,000 casualties in under a week, causing the Germans to dub the battle "Der leichenfeld von Loos" -- or "Field of corpses of Loos."
After the battle, the French lost control of the British forces and General Haig became Commander in Chief of the British Army. Months later, after attending a lecture on the battle of Loos, a young Winston Churchill (who was made a battalion commander in 1916) wrote "They asked what was the lesson of [the battle of Loos]. I restrained an impulse to reply 'don't do it again' -- but they will I have no doubt."