Born on 18 September 1890, Loch was educated at Wellington College and the Royal Military Academy, Woolwich, and upon passing out from the latter, received a commission as a second lieutenant into the Royal Artillery in 1910. He saw action during World War I at the retreat from Mons and the battles of the Marne and Aisne, all in 1914. Leaving the front lines in 1916 he became an instructor in gunnery at the School of Instruction for the Royal Horse Artillery and the Royal Field Artillery until he returned to front line service in the Italian Campaign of 1918. During the war Loch was twice mentioned in dispatches and received the Military Cross (MC).