In the spring, Allied commanders had been concerned about the ability of the French Army to withstand the enormous losses at Verdun. The original plans for an attack around the River Somme were modified to let the British make the main effort. This would serve to relieve pressure on the French, as well as the Russians who had also suffered great losses. On 1 July, after a week of heavy rain, British divisions in Picardy began the Battle of the Somme with the Battle of Albert, supported by five French divisions on their right flank. The attack had been preceded by seven days of heavy artillery bombardment. The experienced French forces were successful in advancing but the British artillery cover had neither blasted away barbed wire, nor destroyed German trenches as effectively as was planned. They suffered the greatest number of casualties (killed, wounded and missing) in a single day in the history of the British Army, about 57,000.