Birch went with his brigade to France in August 1914, serving under the command of Sir Edmund Allenby, in the retreat from Mons and in the battle of the Aisne and Ypres-Armentières. In January 1915 he was appointed brigadier-general on the general staff of the Cavalry Corps, and a few months later C.R.A. of the 7th division going in the same position in July to the I Corps, then commanded by Sir Douglas Haig. In May 1916 Haig brought him to general headquarters as artillery adviser, a post he held until the end of the war. He was promoted lieutenant-general in 1919 when he was made a colonel commandant of the Royal Artillery.