The British summer attack at the Somme took place while the two sides continued to claw at one another at Verdun. Contrary to plans worked out the previous winter, the French could not participate fully in a joint attack. Nonetheless, the British took up their offensive with vast optimism. The new British commander. General Sir Douglas Haig, planned a breakthrough at the Somme based on a prolonged artillery barrage followed by a rapid advance by his forces. Hundreds of thousands of volunteers, many from the nation's upper classes, had poured into military service since 1914. The "New Army" they had formed consisted of raw but enthusiastic divisions, and the Somme offensive was to be their baptism of fire. Cavalry forces were waiting behind the lines to exploit the forthcoming breakthrough and to take the war into a decisive phase in open country. Nothing of the sort occurred. Surviving German machine gunners in the front lines combined with German artillerymen to slaughter the advancing British. Although the first day's assault (on July 1 ) ended with minimal gains and unprecedented casualties—the British loss of 20,000 killed and 40,000 wounded stands as a uniquely bloody set of casualties for a single day in any war—Haig continued the offensive for several months. As at Verdun, the defenders suffered grim losses while the battle line scarcely moved forward or backward. As at Verdun, both sides seemingly absorbed their losses and looked to another year of campaigning in 1917.