 He was a descendant of the noted 18th-century jurist John Erskine of Carnock.Erskine was educated at Charterhouse School and later entered the Royal Military College, Sandhurst and was commissioned as a second lieutenant into the King's Royal Rifle Corps (KRRC) in 1918.He served during World War I in France and Belgium and attended the Staff College, Camberley from 1929 to 1930.