The French part of the offensive was intended to be strategically decisive by breaking through the German defences on the Aisne front within 48 hours, with casualties expected to be around 10,000 men.

The British Third and First armies achieved the deepest advance since trench warfare began, along the Scarpe river in the Battle of Arras, which inflicted many casualties on the Germans, attracted reserves and captured Vimy Ridge to the north.

Fighting known as the Battle of the Observatories continued for local advantage all summer on the Chemin des Dames and along the Moronvilliers heights east of Reims.

After the costly fighting at Verdun and on the Somme in 1916, General Robert Nivelle replaced Marshal Joseph Joffre as the commander of the French armies on the Western Front in December.

[2] The Russian Revolution, the German withdrawal to the Hindenburg Line and the likelihood of a declaration of war by the US, made some assumptions of the plan obsolete.

At a meeting on 6 April, despite the doubts of other politicians, the army group commanders and the British, Alexandre Ribot, the new French Prime Minister supported the plan.

[3][4] Preparing the Nivelle Offensive was a huge and costly undertaking, involving c. 1.2 million troops and 7,000 artillery pieces on a front between Reims and Roye.

The principal effort was an attack on the German positions along the Chemin des Dames ridge, in the Second Battle of the Aisne and an eventual link with the British.

[6] The ground at Brimont began to rise to the west towards Craonne and then reached a height of 180 m (590 ft) along a plateau which continued westwards to Fort Malmaison.

The French held a bridgehead 20 km (12 mi) wide on the north bank of the Aisne, south of the Chemin des Dames, from Berry-au-Bac to Fort Condé on the road to Soissons.

[7] German air reconnaissance was possible close to the front although longer-range sorties were impossible to protect because of the greater number of Allied aircraft.

On 6 April a division was seen encamped near Arras, troop and transport columns crowded the streets while more narrow-gauge railways and artillery were seen to have moved closer to the front.

Ground communication with the German artillery was made more reliable by running telephone lines along steep slopes and deep valleys which were relatively free of French artillery-fire; wireless control stations had been set up during the winter to link aircraft to the guns.

[10] Combatants on both sides claimed the battle was the most psychologically exhausting of the war; recognising this, Pétain frequently rotated divisions, in a process known as the noria system.

While this ensured units were withdrawn before their ability to fight was significantly eroded, it meant that a high proportion of the French army was affected by the battle.

[12] Groupe d'armées du Nord on the northern flank of Groupe d'armées de Reserve (GAR) had been reduced to one army with three corps and began French operations with preliminary attacks by the Third Army on German observation points at St. Quentin on 1–4, 10 and 13 April, which took some of the German defences in front of the Siegfriedstellung (Hindenburg Line) in preliminary operations.

[13] On 9 April the British Third Army attacked to the east of Arras from Croisilles to Ecurie, against Observation Ridge, north of the Arras–Cambrai road and then towards Feuchy and the German second and third lines.

The Third Army attack on the German defences either side of the Scarpe river penetrated 6,000 yd (3.4 mi; 5.5 km), the furthest advance achieved since the beginning of trench warfare.

On the northern flank which faced east near Laffaux, I Colonial Corps was able to penetrate only a few hundred yards into the defences of the Condé-Riegel (Condé Switch Line).

To the east of Vauxaillon at the north end of the Sixth Army, Mont des Singes was captured with the help of British heavy artillery but then lost to a German counter-attack.

[21] On 17 April the Fourth Army on the left of Groupe d'armées de Centre (GAC) began the subsidiary attack in Champagne from Aubérive to the east of Reims which became known as Bataille des Monts, with the VIII, XVII and XII Corps on an 11 km (6.8 mi) front.

General Franchet d'Espèrey called La Malmaison "the decisive phase of the Battle...that began on 16 April and ended on 2 November...".

He was replaced by the considerably more cautious Pétain, with Foch as chief of the general staff; the new commanders abandoned the strategy of decisive battle for one of recuperation and defence, to avoid high casualties and to restore morale.

[33] After the substitution of limited objectives in favour of breakthrough attempts, a French attack on 4 and 5 May by two regiments captured Craonne and took the edge of the Californie plateau but was not able to cross the Ailette River.

The capture of the Dragon's Cave marked the beginning of the Battle of the Observatories proper, which lasted all summer as both sides fought for possession of the high ground on the Chemin des Dames.

Boehn chose to defend the front positions, rather than treat them as an advanced zone and conduct the main defence north of the Canal de l'Oise à l'Aisne.

Gas bombardments on low-lying land near the canal dispersed very slowly and became so dense that the carriage of ammunition and supplies to the front was made impossible.

The French infantry and 21 tanks reached the German second position according to plan; the 38th Division captured Fort de Malmaison and XXI Corps took Allemant and Vaudesson.

[45] In four days the French advanced 9.7 km (6 mi) and forced the Germans off the Chemin des Dames, back to the north bank of the Ailette valley by the night of 1/2 November.

The final objectives were largely gained before dark and British losses in the morning were light, although the planners had expected casualties of up to 50 per cent in the initial attack.