塹壕
Trench warfare prevailed in 1915, and the BEF—as the junior partner on the Western Front—fought a series of small battles, at times coordinated with the larger French offensives, like the Battle of Neuve Chapelle which is always associated with the shell crisis, the Battle of Aubers Ridge, the Battle of Festubert in May and the Battle of Givenchy in June. On 22 April 1915, the German Army launched the Second Battle of Ypres, employing poison gas for the first time on the Western Front and capturing much of the high ground that ringed the salient. By September 1915, the BEF had grown in size with the first of the Kitchener's New Army divisions entering the line, and as part of the Third Battle of Artois, the BEF launched a major attack, the Battle of Loos, utilising its own newly developed chemical weapons for the first time. The resulting failure marked the end for Field Marshal French. On 19 December 1915, General Sir Douglas Haig replaced him as Commander-in-Chief (C-in-C) of the BEF.