March 1916 saw him return to the Western Front. He was allotted to the Fourth Army, which was preparing for an attack in the Somme area. In the pre-battle plans, Horne advocated and became an architect of the "creeping barrage", a tactic that was used for the rest of the war. On 1 July 1916, Horne's XV Corps participated in the costliest battle of the First World War. His force consisted of the 7th and 21st Divisions. They attacked the villages of Fricourt and Mametz, capturing both on the first day although suffering 7,500 casualties in the process.