were withdrawn before their ability to fight was significantly eroded, it meant a high proportion of the French army was affected by the battle. By the beginning of 1917, morale was brittle, even in divisions with good combat records. In December 1916, Robert Nivelle replaced Pétain as commander of French armies on the Western Front and began planning a spring attack in Champagne, part of a joint Franco-British operation. Nivelle claimed the capture of his main objective, the Chemin des Dames, would achieve a massive breakthrough and cost no more than 15,000 casualties. Poor security meant German intelligence was well informed on tactics and timetables, but despite this, when the attack began on 16 April the French made substantial gains, before being brought to a halt by the newly built and extremely strong defences of the Hindenburg Line. Nivelle persisted with frontal assaults and by 25 April the French had suffered nearly 135,000 casualties, including 30,000 dead, most incurred in the first two days. Concurrent British attacks at Arras were more successful, although ultimately of little strategic value. Operating as a separate unit for the first time, the Canadian Corps capture of Vimy Ridge during the battle is viewed by many Canadians as a defining moment in creating a sense of national identity. Although Nivelle continued the offensive, on 3 May the 21st Division, which had been involved in some of the heaviest fighting at Verdun, refused orders to go into battle, initiating the French Army mutinies; within days, acts of "collective indiscipline" had spread to 54 divisions, while over 20,000 deserted. Unrest was almost entirely confined to the infantry, whose demands were largely non-political, including better economic support for families at home, and regular periods of leave, which Nivelle had ended. Although the vast majority remained willing to defend their own lines, they refused to participate in offensive action, reflecting a complete breakdown of trust in the army leadership. Nivelle was removed from command on 15 May and replaced by Pétain, who resisted demands for drastic punishment and set about restoring morale by improving conditions. While exact figures are still debated, only 27 men were actually executed, with another 3,000 sentenced to periods of imprisonment; however, the psychological effects were long-lasting, one veteran commenting "Pétain has purified the unhealthy atmosphere...but they have ruined the heart of the French soldier". The last large-scale offensive of this period was a British