Plan XVII was the name of a "scheme of mobilization and concentration" that was adopted by the French Conseil Supérieur de la Guerre (the peacetime title of the French General Staff) from 1912–1914, to be put into effect by the French Army in the event of war between France and Germany. Though it was not "a prescribed narrative for the campaign" or battle plan, the deployment made possible a prompt invasion of Germany and/or Belgium before Germany could mobilise its reserves, simultaneous to the Russians' invasion of East Prussia. The plan was implemented from 7 August 1914, with disastrous consequences for the French, who were defeated in the Battle of the Frontiers  at a cost of The French northern armies were forced into a retreat as far as the Marne river, where in the First Battle of the Marne  the German armies were defeated and forced back to the Aisne river.