TheHundred Days Offensive (8 August to 11 November 1918) was a series of massiveAllied offensives that ended theFirst World War. Beginning with theBattle of Amiens (8–12 August) on theWestern Front, the Allies pushed theImperial German Army back, undoing its gains from theGerman spring offensive (21 March – 18 July).
The Germans retreated to theHindenburg Line, but the Allies broke through the line with a series of victories, starting with theBattle of St Quentin Canal on 29 September. The offensive led directly to theArmistice of 11 November 1918 which ended the war with an Allied victory. The term "Hundred Days Offensive" does not refer to a planned Allied campaign, but rather the rapid series of Allied victories.
TheGerman spring offensive on theWestern Front had begun on 21 March 1918 withOperation Michael and had petered out by July. TheGerman Army had advanced to theRiver Marne, but failed to achieve their aim of a victory that would decide the war. When the GermanOperation Marne-Rheims ended in July, the Allied supreme commander,Ferdinand Foch, ordered a counter-offensive, which became known as theSecond Battle of the Marne. The Germans, recognizing their untenable position, withdrew from the Marne to the north. For this victory, Foch was granted the titleMarshal of France.
After the Germans had lost their forward momentum, Foch considered the time had arrived for theAllies to return to theoffensive. GeneralPershing who commanded theAmerican Expeditionary Force (AEF) was keen to use his army as an independent force. TheBritish Expeditionary Force (BEF) had been reinforced by large numbers of troops returned from theSinai and Palestine campaign and from theItalian front, and by replacements previously held back in Britain byPrime MinisterDavid Lloyd George.[8]: 155
The military planners considered a number of proposals. Foch agreed to a proposal byField MarshalSir Douglas Haig,commander-in-chief of the BEF, to strike on theRiver Somme, east ofAmiens and south-west of the site of the 1916Battle of the Somme, to force the Germans away from the vitalAmiens–Paris railway.[8]: 472 The Somme was chosen because it remained the boundary between the BEF and the French armies, along the Amiens–Roye road, allowing the two armies to cooperate. ThePicardy terrain provided a good surface fortanks, unlike inFlanders, and the defences of the German2nd Army under GeneralGeorg von der Marwitz were relatively weak, having been subjected to continual raiding by theAustralians in a process termedpeaceful penetration.
The Battle of Amiens (with the French attack on the southern flank called the Battle of Montdidier) opened on 8 August, with an attack by more than 10 Allied divisions—Australian, Canadian, British, and French forces—with more than 500 tanks.[8]: 497 The mastermind of the plan was the Australian Lieutenant GeneralJohn Monash.[9][10] Through careful preparation, the Allies achieved surprise.[11]: 20, 95 [12] The attack, led by the BritishFourth Army, broke through the German lines, and tanks attacked German rear positions, sowing panic and confusion. By the end of the day, a gap 15 mi (24 km) wide had been created in the German line south of the Somme.[13] The Allies had taken 17,000 prisoners and 339 guns. Total German losses were estimated to be 30,000 men, while the Allies had suffered about 6,500 killed, wounded and missing. The collapse in German morale ledErich Ludendorff to dub it "the Black Day of the German Army".[11]: 20, 95
The advance continued for three more days but without the spectacular results of 8 August, since the rapid advance outran the supporting artillery and ran short of supplies.[14] During those three days, the Allies had managed to gain 12 mi (19 km). Most of this was taken on the first day as the arrival of German reinforcements after this slowed the Allied advance.[15] On 10 August, the Germans began to pull out of thesalient that they had managed to occupy during Operation Michael in March, back towards theHindenburg Line.[16]
Haig refused to continue the attack and instead prepared to launch a fresh offensive by theThird Army atAlbert (theBattle 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 FrenchTenth Army starting the Second Battle of Noyon on 17 August, capturing the town ofNoyon on 29 August.[17] On 26 August, to the north of the initial attack, theFirst Army widened the attack by another 7 mi (11 km) with the Second Battle of Arras of 1918.Bapaume fell on 29 August (during theSecond Battle of Bapaume).
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 theBattle 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 theBattle 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 theBattle of the Scarpe (1918) (26 August) and theBattle of Drocourt-Queant Line (2 September).[19]
South of the BEF, the FrenchFirst 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 nearLaon during the Battle of Vauxaillon (14 September).[20]: 125 The British Fourth Army approached the Hindenburg Line along the St Quentin Canal, during theBattle 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.
Foch planned a series ofconcentric attacks on the German lines in France (sometimes referred to as the Grand Offensive), with the various axes of advance designed to cut Germanlateral 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 fromCerny on theAisne river toArras.[21] Before Foch's main offensive was launched, the remaining German salients west and east of the line were crushed atHavrincourt andSt Mihiel on 12 September and at the Battle of Épehy and theBattle 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 theMeuse-Argonne Offensive (this offensive includes the battles of Somme-Py, Saint-Thierry, Montfaucon, and Chesne of 1 November). On 28 September, the Army Group underAlbert I of Belgium (the Belgian Army, the BritishSecond Army and theFrench Sixth Army), attacked nearYpres in Flanders (theFifth 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 theBattle 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 theSecond Battle of Cambrai, with Cambrai itself falling to the Canadians.[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.
Through October, the German armies retreated through the territory gained in 1914. The Allies pressed the Germans back toward the lateral railway line fromMetz toBruges, 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 thePursuit to the Selle (9 October), battles ofCourtrai (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), theSerre (20 October),Valenciennes (1 November),the Sambre (including the Second Battle of Guise) (4 November), and Thiérache (4 November), and thePassage of the Grande Honnelle (5 November), with fighting continuing until theArmistice took effect at 11:00 on 11 November 1918. The last soldier to die wasHenry Gunther, one minute before the armistice came into effect.
