In September 1914, a month after the outbreak of the Great War, he raised and equipped the 11th, 12th, and 13th (Service) Battalions of the Royal Sussex Regiment, who became known as "Lowther's Lambs", and, together with the 14th (Service) Battalion of the Hampshire Regiment, formed the 116th Brigade of the 39th Division. His recruiting was highly successful, enlisting men who were volunteering for Kitchener's Army from the South Downs already bound to one another by community ties. However, Lowther, like most who raised service battalions, was not to command them in action. He returned to Herstmonceux, while his "Lambs", after arriving on the Western Front earlier in the year, were terribly damaged in their first attack on 30 June 1916, intended to divert attention from the offensive on the Somme.