The division began disembarking at Alexandria on 25 September and the bulk (including the East Lancashire Brigade) concentrated at Cairo.

[1] The 126th Brigade participated in the Battle of Krithia Vineyard (6–13 August), where Lieutenant William Thomas Forshaw of the 1/9th Battalion, Manchester Regiment was awarded the Victoria Cross, and then for the rest of 1915 was engaged in trench warfare.

On 42nd Division's front, 1/5th East Lancashires (with its band playing) and 1/10th Manchesters of 126th Brigade led the attack over footbridges laid by the engineers over the River Selle.

The Official History records that 'Very fierce fighting took place on the strongly held railway line, and it was two and a half hours before it was finally mopped up by the companies detailed for the purpose.

[10] After the Selle, 42nd Division was withdrawn into reserve and halted around Beauvois-en-Cambrésis from 24 October until the advance was resumed on 3 November.

In December the division moved into quarters in the Charleroi area and by mid-March 1919 most of its troops had gone home for demobilisation.

[16] Soon after mobilisation, the 4th Battalion, Border Regiment was posted away to become part of 25th Infantry Brigade on lines of communications duties in France.

The 126th Infantry Brigade was constituted as follows during the war:[18] The following officers commanded 126th Infantry Brigade during the war:[18] The 126th Infantry Brigade, under the command of Brigadier Eric Miles DSO MC–a tough but highly competent Regular Army officer of the King's Own Scottish Borderers, with the nickname of "Miles the soldier"–landed, with most of the rest of the division, in France on 15 April 1940 to reinforce the British Expeditionary Force (BEF) on the Franco-Belgian border.

The latter division had, along with the 42nd, initially been held back from reinforcing the BEF sooner to participate in potential operations in Northern Europe, although this plan had never come to fruition and both were sent overseas in the same month.

[19] During the Battle of France in May 1940 42nd Division helped to hold the line of the River Escaut and the canals, until, with the rest of the BEF, it was forced to withdraw to Dunkirk.

[21] After returning to England, the brigade was reorganised and, due to the very heavy losses sustained in France, absorbed large numbers of conscripted men as replacements, most of whom had no prior military experience, and was tasked mainly with coastal and home defence and training in an anti-invasion role to repel a potential German invasion of England.

The invasion never arrived, mainly due to events that happened during the Battle of Britain in the summer of 1940, and the brigade was able to begin training for offensive operations.