 The artillery batteries of I Corps were particularly important because they enfiladed German gun positions behind Vimy Ridge.In total, the British made available to the Canadian Corps twenty-four brigade artillery groups consisting of four hundred and eighty 18 pounder field guns, one hundred thirty-eight 4.5 inch howitzers, ninety-six 2 inch trench mortars, twenty-four 9.45 inch mortars, supported by 245 corps-level siege guns and heavy mortars.This firepower gave a density of one heavy gun for every and one field gun for every of Canadian Corps frontage, representing a considerable average increase, including three times the heavy guns, over the distribution of artillery at the Battle of the Somme a year earlier.