Archibald Campbell Holms MacLean was an officer in the Royal Scots, Royal Flying Corps and Royal Air Force. MacLean attended the Royal Military College Sandhurst before he was commissioned into the Royal Scots. He transferred to the Royal Flying Corps in 1913 and during World War I he served as a squadron and wing commander before taking up senior training and staff appointments. In April 1918 he transferred to the newly formed Royal Air Force and was subsequently promoted to brigadier-general just after the end of World War I.