The attack on Vimy Ridge was spearheaded by the First Army's "shock troops" (the Canadian Corps). The ensuing Battle of Vimy Ridge, the first of a series of actions known as the Battle of Arras was successful: supported by Horne's 1,000-odd artillery pieces, the Canadian forces took the ridge in four days, with approximately 10,000 casualties (against 20,000 German casualties). The capture of Vimy Ridge would prove essential to the British Army: it served as the backbone of the British defence from March 1918 onward.