The attack by the French Tenth Army on Vimy Ridge in May and June had failed, which left the German Sixth Army in control of the high ground below which the French were to have assembled a mass of artillery and infantry. It was agreed that in Artois a Franco-British offensive would be mounted towards Douai, by the French Tenth and the British First armies, co-ordinated by General Foch on a front of between Arras and La Bassée canal. The British First Army was to attack between Grenay and La Bassée canal on a front, with six divisions and three in reserve. The Cavalry Corps and Indian Cavalry Corps were to be held ready to exploit a German collapse. The Franco-British armies were to attack towards Tournai, Valenciennes and Le Quesnoy and subsidiary attacks were to be made by the rest of the Franco-British armies to pin down German reserves.