The Battle of Vimy Ridge was the first instance in which all four Canadian divisions participated in a battle together, as a cohesive formation. The nature and size of the planned Canadian Corps assault necessitated support and resources beyond its normal operational capabilities. Consequently, the British 5th Infantry Division and supplementary artillery, engineer and labour units reinforced the four Canadian divisions already in place. The 24th British Division of I Corps supported the Canadian Corps along its northern flank while the XVII Corps did so to the south. The ad hoc formation, based under I Bavarian Reserve Corps commander Karl Ritter von Fasbender, was the principal defending formation with three divisions responsible for manning the frontline defences opposite the Canadian Corps.