Introduction
Project Habakkuk was a plan by the British during the Second World War to construct an aircraft carrier out of pykrete (a mixture of wood pulp and ice) for use against German U-boats in the mid-Atlantic, which were beyond the flight range of land-based planes at that time. The idea came from Geoffrey Pyke, who worked for Combined Operations Headquarters.
Initial concept
Geoffrey Pyke was an old friend of J.D. Bernal and had been recommended to Lord Mountbatten, Chief of Combined Operations, by the Cabinet minister Leopold Amery. Pyke worked at Combined Operations Headquarters (COHQ) alongside Bernal and was regarded as a genius by Mountbatten.
Pyke conceived the idea of Habbakuk while he was in the United States organising the production of M29 Weasels for Project Plough, a scheme to assemble an elite unit for winter operations in Norway, Romania and the Italian Alps. He had been considering the problem of how to protect seaborne landings and Atlantic convoys out of reach of aircraft cover. The problem was that steel and aluminium were in short supply, and were required for other purposes. Pyke realized that the answer was ice, which could be manufactured for only 1 per cent of the energy needed to make an equivalent mass of steel. He proposed that an iceberg, natural or artificial, be levelled to provide a runway and hollowed out to shelter aircraft.
From New York Pyke sent the proposal via diplomatic bag to COHQ, with a label forbidding anyone apart from Mountbatten from opening the package. Mountbatten in turn passed Pyke's proposal on to Churchill, who was enthusiastic about it.
Pyke was not the first to suggest a floating mid-ocean stopping point for aircraft, nor even the first to suggest that such a floating island could be made of ice. A German scientist, Dr Gerke von Waldenburg, had proposed the idea and carried out some preliminary experiments on Lake Zurich in 1930. The idea was a recurring one: in 1940 an idea for an ice island was circulated around the Admiralty, but was treated as a joke by officers, including Nevil Shute, who circulated a memorandum that gathered ever more caustic comments. The document had to be retrieved just before it reached the First Sea Lord's inbox.
Pykrete
In early 1942 Pyke and Bernal called in Max Perutz to determine whether an icefloe large enough to withstand Atlantic conditions could be built up fast enough. Perutz pointed out that natural icebergs have too small a surface above water for an airstrip, and are prone to suddenly rolling over. The project would have been abandoned if it had not been for the invention of pykrete, a mixture of water and woodpulp that when frozen was stronger than plain ice, was slower-melting and would not sink. It has been suggested that Pyke was inspired by Inuit sleds reinforced with moss.
Pykrete could be machined like wood and cast into shapes like metal, and when immersed in water formed an insulating shell of wet wood pulp on its surface that protected its interior from further melting. However, Perutz found a problem: ice flows slowly, in what is known as plastic flow, and his tests showed that a pykrete ship would slowly sag unless it was cooled to −16 °C (3 °F). To accomplish this the ship's surface would have to be protected by insulation, and it would need a refrigeration plant and a complicated system of ducts.
Perutz proceeded to conduct experiments on the viability of pykrete and its optimum composition in a secret location underneath Smithfield Meat Market in the City of London. The research took place in a refrigerated meat locker behind a protective screen of frozen animal carcasses.
Scale model
The decision was made to build a large-scale model at Jasper National Park in Canada to examine insulation and refrigeration techniques, and to see how pykrete would stand up to artillery and explosives. Large ice blocks were constructed at Lake Louise, Alberta, and a small prototype was constructed at Patricia Lake, Alberta, measuring only 60 by 30 feet (18 metres by 9 metres), weighing 1,000 tons and kept frozen by a one-horsepower motor. The work was done by conscientious objectors who did alternative service of various kinds instead of military service. They were never told what they were building. Bernal informed COHQ that the Canadians were building a 1,000-ton model, and that it was expected to take eight men fourteen days to build it. The Chief of Combined Operations (CCO) responded that Churchill had invited the Chiefs of Staff Committee to arrange for an order to be placed for one complete ship at once, with the highest priority, and that further ships were to be ordered immediately if it appeared that the scheme was certain of success.
The Canadians were confident about constructing a vessel for 1944. The necessary materials were available to them in the form of 300,000 tons of wood pulp, 25,000 tons of fibreboard insulation, 35,000 tons of timber and 10,000 tons of steel. The cost was estimated at £700,000.
Meanwhile Perutz had determined via his experiments at Smithfield Market that the optimum structural properties were given by a mixture of 14 per cent wood pulp and 86 per cent water. He wrote to Pyke in early April 1943 and pointed out that if certain tests were not completed in May, there would be no chance of delivering a completed ship in 1944.
By May the problem of cold flow had become serious and it was obvious that more steel reinforcement would be needed, as well as a more effective insulating skin around the vessel's hull. This caused the cost estimate to increase to £2.5 million. In addition, the Canadians had decided that it was impractical to attempt the project "this coming season". Bernal and Pyke were forced to conclude that no Habbakuk vessel would be ready in 1944.
Pyke was excluded from the planning for Habbakuk in an effort to secure American participation, a decision that Bernal supported. Pyke's earlier disagreements with American personnel on Project Plough, which had caused his removal from that project, were the main factor in this decision.
Naval architects and engineers continued to work on Habbakuk with Bernal and Perutz during the summer of 1943. The requirements for the vessel became more demanding: it had to have a range of 7,000 miles (11,000 km) and be able to withstand the largest waves recorded, and the Admiralty wanted it to be torpedo-proof, which meant that the hull had to be at least 40 ft (12 m) thick. The Fleet Air Arm decided that heavy bombers should be able to take off from it, which meant that the deck had to be 2,000 ft (610 m) long. Steering also raised problems; it was initially projected that the ship would be steered by varying the speed of the motors on either side, but the Royal Navy decided that a rudder was essential. However, the problem of mounting and controlling a rudder over 100 ft (30 m) high was never solved.
Variants
Naval architects produced three alternative versions of Pyke's original concept, which were discussed at a meeting with the Chiefs of Staff in August 1943:
* Habbakuk I (soon discarded) would have been made of wood.
* Habbakuk II was closest to the COHQ model and would have been a very large, slow, self-propelled vessel made of pykrete with steel reinforcement. The size would have been a length of 1200 meters and a width of 180 meters
* Habbakuk III was a smaller, faster version of Habbakuk II.
Air Chief Marshal Portal asked about potential bomb damage to Habbakuk III, and Bernal suggested that a certain amount of deck covering might be ripped off, but could be repaired by some kind of flexible matting. It would be more difficult to deal with bomb holes in the centre portion, though the roof over the aircraft hangars would be made proof against 1,000 kg bombs. Bernal considered that no one could say whether the larger Habbakuk II was a practical proposition until a large-scale model could be completed and tested in Canada in the spring of 1944. He had no doubts about the suitability of pykrete as a material, but said that constructional and navigational difficulties remained to be overcome.
The final design of Habbakuk II gave the bergship (as it was called) a displacement of 2.2 million tons. Steam turbogenerators were to supply 33,000 hp (25,000 kW) for 26 electric motors mounted in separate external nacelles (normal, internal ship engines would have generated too much heat for an ice craft). Its armament would have included 40 dual-barrelled 4.5" DP (dual-purpose) turrets and numerous light anti-aircraft guns, and it would have housed an airstrip and up to 150 twin-engined bombers or fighters.
Shooting incident
According to some accounts, at the Quebec Conference in 1943 Lord Mountbatten brought a block of pykrete along to demonstrate its potential to the admirals and generals who accompanied Winston Churchill and Franklin D. Roosevelt. Mountbatten entered the project meeting with two blocks and placed them on the ground. One was a normal ice block and the other was pykrete. He then drew his service pistol and shot at the first block. It shattered and splintered. Next he fired at the pykrete to give an idea of the resistance of that kind of ice to projectiles. The bullet ricocheted off the block, grazing the trouser leg of Admiral Ernest King, and ended up in the wall.
Sir Alan Brooke's diaries support this account, telling how Mountbatten brought two blocks, one of ice and one of pykrete. After first shooting at the ice, with a warning to beware of splinters, Mountbatten said "I shall fire at the block on the right to show you the difference". Brooke reported that "the bullet rebounded out of the block and buzzed round our legs like an angry bee".
Max Perutz gave an account of a similar incident in his book I Wish I Made You Angry Earlier. A demonstration of pykrete was given at Combined Operations Headquarters (COHQ) by a naval officer, Lieutenant Commander Douglas Grant, who was provided by Perutz with rods of ice and pykrete packed with dry ice in thermos flasks and large blocks of ice and pykrete. Grant demonstrated the comparative strength of ice and pykrete by firing bullets into both blocks: the ice shattered, but the bullet rebounded from the pykrete and hit the Chief of the Imperial Staff (Sir Alan Brooke) in the shoulder. Brooke was unhurt.
End of project
Later in 1943 Habbakuk began to lose priority. Mountbatten listed several reasons:
* Demand for steel for other purposes was too great.
* Permission had been received from Portugal to use airfields in the Azores, which facilitated the hunting of U-boats in the Atlantic
* The introduction of long-range fuel tanks allowed British-based aircraft extra patrol time over the Atlantic
* The numbers of escort carriers were being increased.
* In addition, Mountbatten himself withdrew from the project.
The final meeting of the Habakkuk board took place in December 1943. It was officially concluded that "The large Habbakuk II made of pykrete has been found to be impractical because of the enormous production resources required and technical difficulties involved."
The use of ice had actually been falling out of favour before that, and other ideas for "floating islands" had been considered, such as welding Liberty Ships or landing craft together (Project TENTACLE). It took three hot summers to completely melt the prototype constructed in Canada.
Perutz wrote that he stayed in Washington D.C. while U.S. Navy engineers evaluated the viability of Habbakuk. He concluded: "The U.S. Navy finally decided that Habakkuk was a false prophet. One reason was the enormous amount of steel needed for the refrigeration plant that was to freeze the pykrete was greater than that needed to build the entire carrier of steel, but the crucial argument was that the rapidly increasing range of land-based aircraft rendered floating islands unnecessary."
Name: HMS Habakkuk
Type: Pykrete Super Aircraft Carrier
Displacement: 2,000,000 tons
Length: 2000 feet (609.6 metres)
Width: 300 feet (91.3 metres)
Aircraft: Up to 150 fighters or bombers.
