The first attack of the Grand Offensive was launched on 26 September by the French and the AEF in the Meuse-Argonne Offensive (this offensive includes the Battle of Somme-Py, the Battle of Saint-Thierry, the Battle of Montfaucon, and the Battle of Chesne of 1 November). On 28 September, the Army Group under Albert I of Belgium (the Belgian Army, the British Second Army and the French Sixth Army), attacked near Ypres in Flanders (the Fifth Battle of Ypres). Both attacks made good progress initially but were then slowed by supply difficulties. The Grand Offensive involved attacking over difficult terrain, resulting in the Hindenburg Line not being broken until 17 October.