September 1917 saw the end of the 1st Battalion’s work in the Ypres area as on the 21st, the 47th Division moved south to join the 1st Army near Arras. On 19th November 1917, orders were received to move again to prepare for the battle of Bourlon Wood.
In the spring the Germans had retired to the newly constructed Hindenburg Line methodically destroying everything as they went. The region, in which the London Irish found itself was one of utter devastation. The Hindenburg Line consisted of a heavily wired continuous line of entrenchments, which comprised all the high ground west of Cambrai.
After pushing back the enemy to this line, nothing had been done until 20th November, when the British opened a surprise attack supported by a large number of tanks that swept through the wire of the Hindenburg Line as far as Bourlon Wood. From this position on high ground, one had excellent observation of Cambrai. In consequence, attack and counter attack followed one another for a week, the village changing hands daily. The casualties on both sides had been heavy and the issue still hung in the balance.
On taking over at Bourlon Wood on 28th/29th November, the London Irish were bombarded with gas shells causing many casualties. On 30th November, the enemy made another counter attack in force, followed by a heavy bombardment. This action became the greatest defensive battle in which the London Irish were to take part until the great retreat in March 1918. Ground was only yielded under extreme pressure and successful counter attacks were soon initiated but the flanks of the Division were not secure and eventually it was decided to evacuate Bourlon Wood and withdraw to the security of the Hindenburg Line. This was carried out successfully on the night of 4th December.
Casualties in the six days of fighting had been heavy, the dead being Lieut Tolson, 2/Lieut Young. 2/Lieut Aird and about 50 other ranks. Other battalions had suffered even more heavily. The enemy gas in Bourlon Wood hung in the trees and bushes so thickly that everyone was compelled to wear respirators continuously. But digging in, respirators become difficult and without the cover of deep trenches, the persistent shell fire took its toll. The general outcome of these heavy casualties was that all infantry brigades were reduced from four to three battalions. The three weakest battalions were broken up, namely the 6th, 7th and 8th battalions of the London Regiment. The 6th (City of London Rifles) sent 6 officers and 170 other ranks to the London Irish.
Read more here from the Regimental History.