were successful. 1953 feasibility study In 1953, the National Research Council of Canada commissioned a feasibility study on the idea of planting a large explosive charge underneath the peaks by drilling vertical and horizontal shafts from Maud Island in the sound. Based on the study, this approach was recommended. Dolmage and Mason Consulting Engineers were retained to plan the project, and three firms, Northern Construction Company, J.W. Stewart Limited and Boyles Brothers Drilling Company, were granted the contract, which cost in excess of 3 million Canadian dollars (equivalent to $ CAD in 2018). Although not planned as a test for nuclear weapons purposes, this large underground explosion at Ripple Rock was of interest to nuclear weapons scientists at the United Kingdom's Atomic Weapons Research Establishment at Aldermaston, which sent a delegation to Canada and set up various monitoring instruments to record data from the explosion. Little more is known of their objectives, although there are detailed accounts in two declassified documents in the National Archives in London. Explosion Between November 1955 and April 1958, a three-shift operation involving an average of 75 men worked to build of vertical shaft from Maud Island, of horizontal shaft to the base of Ripple Rock, and two main vertical shafts up into the twin peaks, from which "coyote" shafts were drilled for the explosives. The contract was awarded to two firms for $2,639,000. At the time of the contract it was estimated the tunnels and shafts would not be completed until either 1957 or 1958. 1,270 metric tonnes of Nitramex 2H explosive was placed in these shafts, estimated at ten times the amount needed for a similar explosion above water. The explosion took place at 9:31:02 am on 5 April 1958. 635,000 metric tons of rock and water were displaced by the explosion, spewing debris at least 300 metres in the air which fell on land on either side of the narrows. The blast increased the clearing at low tide to about 14 metres (45 feet). After this, its two peaks were 13.7 m (45 ft) and 15.2 m (50 ft) underwater. The Royal Canadian Mounted Police had cleared the area of people within of the explosion, and the engineers and TV crew that witnessed the explosion were housed in a bunker. The explosion was noted as one of the largest non-nuclear planned explosions on record, though Soviet authorities reported a larger explosion in