 A large-scale trench raid on 13 February 1917, involving 900 men from the 4th Canadian Division, resulted in 150 casualties.An even more ambitious trench raid, using chlorine gas, on 1 March 1917, once again by the 4th Canadian Division, failed and resulted in 637 casualties including two battalion commanders and a number of company commanders killed.This experience did not lessen the extent to which the Canadian Corps employed trench raiding with raids being conducted nightly between 20 March and the opening of the offensive on 9 April, resulting in approximately 1,400 additional Canadian casualties.