By 1917, the size of the British Army on the Western Front had grown to two-thirds the total numbers in the French forces. In April 1917 the BEF began the Battle of Arras. The Canadian Corps and the 5th Division, attacked German lines at Vimy Ridge, capturing the heights and the First Army to the south achieved the deepest advance since trench warfare began. Later attacks were confronted by German reinforcements defending the area using the lessons learned on the Somme in 1916. British attacks were contained and, according to Gary Sheffield, a greater rate of daily loss was inflicted on the British than in "any other major battle."