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Britain had plans for a unique and virtually unsinkable aircraft carrier in World War II. The Habbakuk (a clerk's misspelling of the biblical prophet Habakkuk) would have been 2,000 feet long, 300 feet wide - and made entirely from blocks of ice reinforced with wood pulp. Onboard refrigeration plants would keep the hull frozen. The aim was to provide air cover for ship convoys in the North Atlantic Ocean. A 60-foot-long model of the Habbakuk was built in Lake Jasper in Alberta in 1943. The test was a success, but by then the ice ship was not needed. German U-boats were no longer such a threat. The refrigeration units were turned off that August, and the supercarrier prototype simply melted.
Sources: www.shipwreckcentral.com; www.combinedops.com; www.mysteriesofcanada.com.