After a day at Havre the move was continued—motor transport sections by road and cable sections by train—to Vignacourt. At this village in the Somme Valley, between Abbeville and Amiens, the headquarters of the newly constituted XV. Corps was concentrating under Lieutenant-General Horne, and Major Harrison, on the 23rd April, was appointed Assistant Director of Army Signals—_i.e._ Staff Officer for Signals to the Corps Commander. The Company now became the XV. Corps Signal Company, and served continuously with that Corps throughout the remainder of the war. A few days later the Corps moved into line between the III. and XIII. Corps, becoming a part of the Fourth Army under General Sir H. Rawlinson, and took over the sector fronting Fricourt and Mametz, between Bécourt and Carnoy. On the 30th April the Company took over from the XIII. Corps Signal Company at Heilly, a village on the Ancre, near Corbie. B.F. and B.G. sections were sent to join the headquarters of the two divisions in line—the 7th and 21st respectively—and B.F. section proceeded to Ville-sur-Ancre, where Brigadier-General Napier, commanding the Corps Heavy Artillery, had his headquarters, and took charge of the Heavy Artillery’s communications on the 27th April. The experience of previous battles had shown that, next to an adequate artillery, the primary technical condition for a successful offensive was good and reliable communication between the assaulting infantry, the directing staffs, and the supporting artillery. Overground wires, no matter how multiplied, failed immediately under the counter-barrage. Visual signalling, slow at the best, was generally ineffective because of the smoke and dust of the barrage, the exposure of the _personnel_, and the unsuitability of the terrain, so faith was now pinned on cables laid in deep trenches for thousands of yards in rear of the front line, carrier pigeons, and runners. As soon as the area could be thoroughly surveyed, a programme of work was drawn up covering:— (_a_) Reconstruction of and additions to the inadequate open wire routes in the back area, from Corps headquarters up to behind Méaulte, Morlancourt, and the Bois des Tailles, sufficient to cope with the number of units and formations to be thrown in for the battle, and suitably designed and located for rapid extension along the probable roads of the anticipated advance. (_b_) A complete network of cable trenches extending from the heads of the open wire routes to the front line, providing telephone communication down to company and battery command posts and artillery observation posts.