Cape Spear is the eastern most point in Canada (and outside of Greenland and the western part of Iceland) the most western point in North America, so Newfoundland played a significant role as a transport point for men and equipment bound for Europe.
The harbour at St John's Newfoundland was a point where convoys to cross the North Atlantic were assembled, so a couple of camouflaged gun emplacements at Cape Spear, which is just south of St John's were set up as part of the defense of the harbour. This is one of the two large guns that were installed here.