The 3rd Canadian Tunnelling Company was one of the tunnelling companies of the Canadian Military Engineers during World War I. The tunnelling units were occupied in offensive and defensive mining involving the placing and maintaining of mines under enemy lines, as well as other underground work such as the construction of deep dugouts for troop accommodation, the digging of subways, saps (a narrow trench dug to approach enemy trenches), cable trenches and underground chambers for signals and medical services.