The Nivelle offensive (16 April – 9 May 1917) was a Franco-British operation on the Western Front in the First World War which was named after General Robert Nivelle, the commander-in-chief of the French metropolitan armies, who led the offensive. 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. A preliminary attack was to be made by the French Third Army at St Quentin and the British First, Third and Fifth armies at Arras, to capture high ground and divert German reserves from the French fronts on the Aisne and in Champagne. The main offensive was to be delivered by the French on the Chemin des Dames ridge (the Second Battle of the Aisne). A subsidiary attack was to be made by the Fourth Army (the Third Battle of Champagne). The final stage of the offensive was to follow the meeting of the British and French armies, having broken through the German lines, to pursue the defeated German armies towards the German frontier. The Franco-British attacks were tactically successful; the French Third Army of Groupe d'armées du Nord (GAN, Northern Army Group) captured the German defences west of the Hindenburg Line (Siegfriedstellung) near St Quentin from 1 to 4 April, before further attacks were repulsed. 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. The main French offensive on the Aisne began on 16 April and also achieved considerable tactical success but the attempt to force a strategically decisive battle on the Germans was a costly failure and by 25 April the main offensive had been suspended. The failure of the Nivelle strategy and the high number of French casualties led to mutinies, the dismissal of Nivelle, his replacement by Philippe Pétain and the adoption of a defensive strategy by the French, while their armies recuperated and rearmed.