In early 1917 Vimy Ridge, one of the most important features on the Western Front, was considered impregnable. However, in a spectacular victory, the four Divisions of the Canadian Army Corps, under Lieutenant-General Sir Julian Byng, took almost the entire ridge in a day. This book examines every aspect of the secret to their success: preparation. The author shows how effective observation, accurate shelling, and new infantry tactics all prepared the ground for Byng's victory. When the attack opened at 5.30am on April 9 the Canadians easily overwhelmed the forward fire trenches, secured most of the ridge within the day, and all their planned objectives within four days.