Between 1918 and the period after World War II, Canadian National modernized its steam locomotive fleet by replacing many of the units it received from its constituent railways. MLW was a major beneficiary of these purchases, along with the Canadian Locomotive Company of Kingston, Ontario. MLW grew substantially during the Second World War when its plant facilities were converted primarily to fabricating matériel for the Commonwealth/Allied war effort (largely by a female workforce), including the Ram tank and the Sexton self-propelled gun.