 During 1915, he toured with Benson and appeared with him at London's Court Theatre in December as Lysander in "A Midsummer Night's Dream".During the First World War, Rathbone was called up in 1915 via the Derby Scheme into the British Army as a private with the London Scottish Regiment, joining a regiment that also included his future professional acting contemporaries Claude Rains, Herbert Marshall and Ronald Colman at different points through the conflict.After basic training with the London Scots in early 1916 he received a commission as a lieutenant in the 2/10th Battalion of the King's Liverpool Regiment (Liverpool Scottish), where he served as an intelligence officer and attained the rank of captain.