In 1915 the British army had carried out battles notably at Neuve Chappel in March and after that Aubers Ridge. Lessons were being learnt and expanded on, but there was still much to be done. The attacks at 2nd Ypres, by the Germans and the subsequent debates had seen the end of General Sir Horace Smith-Dorrien's service on the western front as his relationship worsened with Sir John French. Ironically the reputation of French was also waning, with many of his staff and Generals losing faith in him. Some even resorted to going behind his back to apply pressure in having him removed.(1)
The Battle of Loos was not the idea of the British high command, but a French one to aid them in their ventures. Both Sir John French and Sir Douglas Haig, commander of 1st Army tasked with the battle, were not confident with the ground. Both men however were committed to the battle by political and military pressure. General Haig would eventually gain a confidence for the battle, seeing the new gas weapon, used initially by the Germans at 2nd Ypres, and now put into service by the British, as being a weapon that he put much faith in. In fact too much faith, believing that the use of gas could make up for the lack of artillery that befell the BEF during 1915.
For Sir John French the battle of Loos was a cross roads for him, he was an old soldier, an old commander and was in all reality left behind by the new forms of warfare. His high tide had been in the Boer War. However he was caught between feeling the loss of men and still wanting to keep his position and reputation. It was with this conundrum that he agreed reluctantly to the use of the BEF at Loos.
Sir Douglas Haig was tasked with drawing up the plans for the attack. He would use Lt. General Sir Henry Rawlinson’s IV Corps and Lt. General Hubert Gough's I Corps, a total of six divisions with the cavalry being kept in reserve to exploit the expected breakthrough. To argument this force Sir John French kept VI Corps in GHQ reserve, comprising of the newly formed Guards Division and the inexperienced, recently arrived New Army Divisions, 21st and 24th. It is the use and commitment of this reserve of which 21st division played a key part that has caused controversy since with the eventual result being the removal of Sir John from command of the BEF and the rise of Sir Douglas Haig to the command of British Forces in France and Flanders.
(1) Sir Douglas Haig and Sir William Robertson (C of S to Sir John) were two of a few who constanly kept in written touch with the King by letters and reports. Later these two men, for better or worse, depending on your outlook, would control the army through some of the greatest and costly battles it has ever thought.