Hundred Days Offensive

Advance in Picardy

Somme

On 15 August, Foch demanded that Haig continue the Amiens offensive, even though the attack was faltering as the troops outran their supplies and artillery and German reserves were being moved to the sector^{[citation needed]}. Haig refused and prepared to launch a fresh offensive by the Third Army at Albert (the Battle of Albert), which opened on 21 August.^{[8]: 713–4} The offensive was a success, pushing the German 2nd Army back over a 34 mi (55 km) front. Albert was captured on 22 August.^[17] The attack was widened on the south, by the French Tenth Army starting the Second Battle of Noyon on 17 August, capturing the town of Noyon on 29 August.^[17] On 26 August, to the north of the initial attack, the First Army widened the attack by another 7 mi (11 km) with the Second Battle of Arras of 1918. Bapaume fell on 29 August (during the Second Battle of Bapaume).

Advance to the Hindenburg Line

With the front line broken, a number of battles took place as the Allies forced the Germans back to the Hindenburg Line. East of Amiens (after the Battle of Amiens), with artillery brought forward and munitions replenished, the Fourth Army also resumed its advance, with the Australian Corps crossing the Somme River on the night of 31 August, breaking the German lines during the Battle of Mont Saint-Quentin.^[18] On 26 August, to the north of the Somme, the First Army widened the attack by another 7 mi (11 km) with the Second Battle of Arras of 1918, which includes the Battle of the Scarpe (1918) (26 August) and the Battle of Drocourt-Queant Line (2 September).^[19]

South of the BEF, the French First Army approached the Hindenburg Line on the outskirts of St. Quentin during the Battle of Savy-Dallon (10 September),^{[20]: 128–9} and the French Tenth Army approached the Hindenburg Line near Laon during the Battle of Vauxaillon (14 September).^[20]: 125 The British Fourth Army approached the Hindenburg Line along the St Quentin Canal, during the Battle of Épehy (18 September). By 2 September, the Germans had been forced back close to the Hindenburg Line from which they had launched their offensive in the spring.

Battles of the Hindenburg Line

Foch planned a series of concentric attacks on the German lines in France (sometimes referred to as the Grand Offensive), with the various axes of advance designed to cut German lateral communications, intending that the success of an attack would enable the entire front line to be advanced.^{[11]: 205–6} The main German defences were anchored on the Hindenburg Line, a series of defensive fortifications stretching from Cerny on the Aisne river to Arras.^[21] Before Foch's main offensive was launched, the remaining German salients west and east of the line were crushed at Havrincourt and St Mihiel on 12 September and at the Battle of Épehy and the Battle of the Canal du Nord on 27 September.^[11]: 217

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 battles of Somme-Py, Saint-Thierry, Montfaucon, and 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.^[22]

On 29 September, the central attack on the Hindenburg Line commenced, with the British Fourth Army (with British, Australian and American forces)^[23] attacking in the Battle of St Quentin Canal and the French First Army attacking fortifications outside St Quentin. By 5 October, the Allies had broken through the entire depth of the Hindenburg defences over a 19 mi (31 km) front.^[20]: 123 General Rawlinson wrote, "Had the Boche [Germans] not shown marked signs of deterioration during the past month, I should never have contemplated attacking the Hindenburg line. Had it been defended by the Germans of two years ago, it would certainly have been impregnable…."

On 8 October, the First and Third British Armies broke through the Hindenburg Line at the Second Battle of Cambrai.^[24] This collapse forced the German High Command to accept that the war had to be ended. The evidence of failing German morale also convinced many Allied commanders and political leaders that the war could be ended in 1918; previously, all efforts had been concentrated on building up forces to mount a decisive attack in 1919.

Subsequent operations

Through October, the German armies retreated through the territory gained in 1914. The Allies pressed the Germans back toward the lateral railway line from Metz to Bruges, which had supplied the front in northern France and Belgium for much of the war. As the Allied armies reached this line, the Germans were forced to abandon increasingly large amounts of heavy equipment and supplies, further reducing their morale and capacity to resist.^[26]

The Allied and German armies suffered many casualties. Rearguard actions were fought during the Pursuit to the Selle (9 October), battles of Courtrai (14 October), Mont-d'Origny (15 October), the Selle (17 October), Lys and Escaut (20 October) (including the subsidiary battles of the Lys and of the Escaut), the Serre (20 October), Valenciennes (1 November), the Sambre (including the Second Battle of Guise) (4 November), and Thiérache (4 November), and the Passage of the Grande Honnelle (5 November), with fighting continuing until the Armistice took effect at 11:00 on 11 November 1918. The last soldier to die was Henry Gunther, one minute before the armistice came into effect.