The new French Chief of Staff, Robert Nivelle, had strong-armed through an audacious plan to ‘end the war in two days’ over the objections of the British Chief of Staff, General Haig and the French War Minister. On 16 April 1917 French divisions mounted a simultaneous assault on a 50-mile (80-km) front. But the Germans held well-fortified positions on high ground, and massive casualties were incurred, including the loss of 150 French tanks. Nevertheless, part of the German defensive line was taken, and the accompanying British offensive made the deepest inroads since the start of trench warfare, including capturing Vimy Ridge. The aftermath was devastating. In May, there were mass mutinies in the French army, and on 16 May Nivelle was ignominiously sacked and replaced by the more cautious Petain with a mandate to restore order and morale.