Jabberwalker Jabberwalker:
They say that the initial bombardment of Vimy Ridge by our artillery had the frequency of an idling automobile engine and it went on for about ten minutes. That's a lot of shells raining down in a short period of time. This sort of thing happened on and off for all four years.
[BTW, one of my grandfathers worked as a shell inspector during WWI.]
I'm not too sure about the 10 minutes, it was actually something like 3 weeks and during the assault the troops went forward under a creeping barrage as noted below.
$1:
The attack was to be supported by a massive artillery bombardment. Byng was given all of the First Armies heavy artillery, giving the Canadian Corps close to 1,000 guns. The bombardment began on 20 March and lasted for 20 days. The pace of the bombardment varied during those twenty days, to prevent the Germans working out when the main attack was due. On 3 April the intensity of the bombardment was increased. The last week before the attack was known to the Germans as the “week of suffering”.
http://www.historyofwar.org/articles/battles_vimy_ridge.html$1:
Beginning at exactly 5:30 a.m on Easter Monday, 9 April 1917, the Canadian artillery unleashed a massive barrage on the German positions on Vimy Ridge. The shelling was meticulous in its timing and devastating in its intensity . The targets were specific: artillery and machine gun emplacements and wire entanglements. Lt.-Col. D.E. Macintyre later recalled: "The sustained uproar of this combined and concentrated bombardment was so violent that it quaked the earth for miles... An Air Force observer of this battle later told me that the overhead canopy of our artillery fire was so dense that he saw a number of our low-flying aircraft explode like clay pigeons as they collided with shells in flight. It was like flying through a storm of gigantic and deadly hailstones." After the initial bombardment, the Canadian troops surged forward behind a protective curtain of artillery fire, employing the creeping barrage. The assault overwhelmed the German defences. Despite 10,602 casualties, of whom 3,600 would die, the Canadians succeeded where the British and French had failed: they took Vimy Ridge.
http://www.lermuseum.org/en/canadas-military-history/first-world-war/battlefront-1917/vimy-ridge/