9 April
The attack was to begin at 5:30 am on Easter Monday, 9 April 1917. The attack was originally planned for the morning of 8 April (Easter Sunday), but it was pushed back 24 hours at the request of the French. During the late hours of 8 April and early morning of 9 April the men of the leading and supporting wave of the attack were moved into their forward assembly positions. The weather was cold and later changed to sleet and snow. Although physically discomforting for everyone, the north-westerly storm provided some advantage to the assaulting troops by blowing snow in the faces of the defending troops. Light Canadian and British artillery bombardments continued throughout the prior night but stopped in the few minutes before the attack, as the artillery recalibrated their guns in preparation for the synchronized barrage. At exactly 5:30 am, every artillery piece at the disposal of the Canadian Corps began firing. Thirty seconds later, engineers detonated the mine charges laid under no man's land and the German trench line, destroying a number of German strong points and creating secure communication trenches directly across no man's land. Light field guns laid down a barrage which advanced in predetermined increments, often 100 yards (91 m) every three minutes, while medium and heavy howitzers established a series of standing barrages further ahead, against known defensive systems. During the early fighting the German divisional artilleries, despite heavy losses, were able to maintain their defensive firing. As the Canadian assault advanced, it overran many of the German guns because there was no means of moving them to the rear on account of many of the horses being killed in the initial gas attack.
The 1st, 2nd and 3rd Canadian Divisions reported reaching and capturing their first objective, the Black Line, by 6:25 am. The 4th Canadian Division encountered a great deal of trouble during its advance and was unable to complete its first objective until some hours later. After a planned pause, during which time the 1st, 2nd and 3rd Canadian Divisions consolidated their positions, the advance resumed. Shortly after 7:00 am, the 1st Canadian Division captured the left half of its second objective, the Red Line, and moved the 1st Canadian Brigade forward to mount an attack on the remainder. The 2nd Canadian Division reported reaching the Red Line and capturing the town of Les Tilleuls at approximately the same time. A mine explosion that killed many German troops of the Reserve Infantry Regiment 262 manning the front line preceded the advance of the 3rd Canadian Division. The remaining German troops could do no more than man temporary lines of resistance until later manning a full defence at the German third line. As a result, the southern section of the 3rd Canadian Division's was able to reach the Red Line at the western edge of the Bois de la Folie at around 7:30 am. At 9:00 am the division learned of its exposed left flank, as the 4th Canadian Division had not yet captured Hill 145. The 3rd Canadian Division was thus called upon to establish a divisional defensive flank to its north. Although the Germans commanders were able to maintain open lines of communication and issue operating orders, even with swift staff work the tempo of the assault was such that German decision cycle was unable to react decisively.
The only portion of the Canadian assault that did not go as planned was the advance of the 4th Canadian Division which collapsed almost immediately after exiting their trenches. The commanding officer of one of the assaulting battalions requested that the artillery leave a portion of German trench undamaged. Machine-gun nests in the undamaged sections of the German line pinned down, wounded or killed much of the 4th Canadian Division's right flank. The progress on the left flank was eventually impeded by harassing fire from the "Pimple" which was made worse when the creeping barrage got too far ahead of the advancing troops. In view of the German defence, the 4th Canadian Division did not attempt a further frontal assault throughout the afternoon. Reserve units from the 4th Canadian Division came forward and once again attacked the German positions on the top of the ridge. Persistent attacks eventually forced the German troops holding the south-western portion of Hill 145 to withdraw, but only after they had run out of ammunition, mortars rounds and grenades.
Towards midday, the 79th Reserve Division was ordered to recapture the portions of its third line lost during the progression of the Canadian attack. However, it was not until 6:00 pm that the force was able to organize and counterattack, clearing the Canadian Corps troops out of the ruined village of Vimy, but not recapturing the third line south of the village. By night time, the German forces holding the top of the ridge believed they had overcome the immediate crisis for the mean time. Additional German reinforcements began arriving and by late evening portions of the 111th Infantry Division occupied the third line near Acheville and Arleux, with the remainder of the division arriving the following day.
10 April
The British moved three fresh brigades up to the Red Line by 9:30 am on 10 April to support the advance of the 1st and 2nd Canadian Division, whereupon they were to leapfrog existing units occupying the Red line and advance to the Blue Line. Fresh units including two sections of tanks and the 13th British Brigade were called up from reserve to support the advance on the 2nd Canadian Division. By approximately 11:00 am, the Blue Line, including Hill 135 and the town of Thélus, had been captured. To permit the troops time to consolidate the Blue Line, the advance halted and the barrage remained stationary for 90 minutes while machine guns were brought forward. Shortly before 1:00 pm, the advance recommenced with both the 1st and 2nd Canadian Divisions reporting their final objective. The tank supported advance via Farbus, and directed at the rear of the 79th Reserve Division, was eventually halted by concentrated German fire short of the village. The Canadian 1st and 2nd Divisions were nonetheless able to secure the Brown Line by approximately 2:00 pm.
The 4th Canadian Divison made an attempt to capture the northern half of Hill 145 at around 3:15 pm, briefly capturing the peak before a German counterattack retook the position. The Germans occupying the small salient on ridge soon found themselves being attacked along their flanks by continuously reinforced Canadian Corps troops. When it became obvious that the position was completely outflanked and there was no prospect of reinforcement, the German troops pulled back. The German forces were evacuated off the ridge with German artillery batteries moved west of the Vimy–Bailleul railway embankment or to the Oppy–Méricourt line. By nightfall of 10 April, the only Canadian objective not yet achieved was the capture of the "Pimple".
12 April
The 4th Canadian Division faced difficulties at the start of the battle that forced it to delay its assault on the "Pimple" until 12 April. The "Pimple" was initially defended by the 16th Bavarian Infantry Division, but the Canadian Corps' preliminary artillery bombardment leading up to the assault on 9 April caused heavy casualties amongst its ranks. On 11 April, the 4th Guard Division first reinforced and then relieved affected 16th Bavarian Infantry Division units. The night before the attack, artillery harassed German positions while a gas section of Royal Engineers, employing Livens Projectors, fired more than 40 drums of gas directly into the town of Givenchy-en-Gohelle to cause confusion. The defending German troops managed to drive back the initial Canadian assaults at around 4:00 am using small arms fire. The 10th Canadian Brigade attacked once again at 5:00 am, this time supported by a significant amount of artillery and the 24th British Division of I Corps to the north. The German defensive artillery fire was late and too light to cause the assaulting troops great difficulty, allowing the Canadian Corps to exploit wide gaps and break into the German positions. The 10th Canadian Brigade, assisted by snow and a Westerly wind, fought hastily entrained German troops to capture the entire "Pimple" by 6:00 pm.