An Airport Made Of Ice?
In late September 1942, as German U-boats inflicted heavy damage on Allied ships, Geoffrey Pyke—a science adviser to Britain’s chief of combined operations, Lord Mountbatten—proposed building aircraft carriers of ice, to patrol against submarines and carry planes to battle. These “berg ships,” as he called them, would be virtually unsinkable: How do you sink an ice cube? External insulation would guard against evaporation, and forced circulation of cold air would prevent melting.
Pyke called the proposed project Habbakuk, after a remark about the biblical prophet of that name (which Pyke or his typist misspelled) attributed to Voltaire: “Habakkuk was capable of anything.” The ships would be made not of ordinary ice but of “pykrete,” a frozen mixture of water and wood pulp that had recently been developed and named in Pyke’s honor. Pykrete had much greater tensile strength and resistance to fracture and melting than plain ice. (After the war, it was learned that this idea was not entirely original: Eskimos had long built igloos from a form of pykrete made by reinforcing compressed snow with twigs and moss.)
In December 1942, Winston Churchill urged “the prompt examination of these ideas” and suggested that berg ships might be made from natural ice. In fact, Pyke and his associates in Canada, Britain, and the United States had been conducting research along these lines for about a year. The British iceresearch team was led by Max Perutz, who twenty years later would win a Nobel Prize for elucidating the structure of hemoglobin.
The results were not promising. Ordinary ice was far too brittle and soft for ordinary marine wear and tear, let alone the stresses of combat. Moreover, to function as an aircraft carrier, a berg ship would require a runway almost 2,000 feet long and 200 feet wide, and would have to rise 50 feet above the water and have walls 40 feet thick to withstand waves and enemy artillery. The requisite volume of ice would have a displacement of 2.2 million tons, or 26 times that of the Queen Elizabeth , then the world’s largest ship. No known natural ice formation was anywhere near that big. The berg ships would have to be man-made, and from pykrete, not ice (though research continued on pure ice as well as composites containing straw, cotton, wool, paper, wood strips, and sawdust).
To assess the structural properties of pykrete, researchers measured the modulus of rupture of beams in flexure as well as mechanical strength in compression and tension. To predict damage from torpedoes, .303-caliber bullets were fired from rifles. A 1/50 scale model of a berg ship was constructed at Patricia Lake in Jasper National Park, in Alberta, in March 1943.
As project engineers looked more closely at the logistics of building a full-size berg ship, the idea came to seem increasingly poor. No accessible location would provide enough natural cooling to mass-produce the ships, so vast amounts of refrigeration apparatus would be needed. Furthermore, the Allies now had long-range planes that made large numbers of aircraft carriers unnecessary, especially since Portugal had decided to let the Allies build air bases in the Azores. The new planes required runways so long that they would have made the 2,000-foot berg ship obsolete before one had been built. Moreover, the decline of Germany’s U-boat fleet after mid-1943 made the berg ships’ projected role in antisubmarine warfare less important. Since the American war in the Pacific was progressing faster than expected, the need for such an enormous undertaking as Habbakuk had disappeared. In January 1944, the three nations involved agreed to abandon the project.
