In 1915, the Canadian Corps was little more than a rabble of enthusiastic amateurs. Yet by 1917-18, it had become an accomplished professional fighting force, one characterized by Denis Winter as “much the most effective unit in the BEF” and by Shane Schreiber as “the shock army of the British Empire.” While Canadian military historians have studied this evolution extensively few have examined the decisive element in the transformation—the development of a cadre of proficient senior combat officers. No one questions Currie’s status as Canada’s best fighting general, but of the supporting team he and his predecessor, General Byng, assembled we know precious little. Who, then, were the men commanding the Corps’ four divisions, 12 infantry brigades and supporting machine gun and artillery units—the senior officers whose abilities as trainers and fighters were integral to the CEF’s battlefield success?