On 27 May 1917 around 30,000 French infantry soldiers upped and left their front line trenches on the Western Front. They were mostly battle-hardened veterans who had had enough of their high command’s orders for increasingly futile attacks. They didn’t harm their officers, they just refused to return to the trenches.

The French military authorities, alarmed by news of the Bolshevik revolution in Russia, responded swiftly and decisively: mass arrests followed by mass trials. There were around 3,500 courts-martial; around 23,000 men were convicted of some form of mutiny, of whom around 550 were sentenced to death. It is thought that only around 30-50 men were actually shot, while the rest were jailed. The numbers are sketchy because of the 100 year secrecy order placed on the details by a French government nervous of shattering morale across the country. In fact, the scale of the mutinies were not revealed until later in the twentieth century.

More info here: http://en.wikipedia.org/wiki/French_Army_Mutinies