Editing Project Habakkuk (section)

=== 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)|Lake Louise, Alberta]], and a small prototype was constructed at [[Patricia Lake (Alberta)|Patricia Lake, Alberta]], measuring  60 by 30 feet (18 metres by 9 metres), weighing 1,000 tons and kept frozen by a one-horsepower motor.<ref name="cabinet" /> 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.<ref>{{cite news|url = http://www.mennonitehistorian.ca/29.3.MHSep03.pdf|page= 4|title= War Ship, Ice Blocks and Mennonite COs |first = Donovan |last = Giesbrecht|work = Mennonite Historian|volume= 29|number = 3|date = September 2003}}</ref>  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 [[Fiberboard|fibreboard]] insulation, 35,000 tons of timber and 10,000 tons of steel. The cost was estimated at £700,000.<ref name="brown" />

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 [[Creep (deformation)|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 grow 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 Habakkuk vessel would be ready in 1944.<ref name="brown" />

Pyke was excluded from the planning for Habakkuk 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.<ref name=adelman>{{cite book |last=Adelman |first=Robert H. |author2=George Walton |title=''The Devil's Brigade'' |publisher=Naval Institute Press |year=2004 |isbn=1-59114-004-8}}</ref>

[[Naval architect]]s and engineers continued to work on Habakkuk with Bernal and Perutz during the summer of 1943. The requirements for the vessel became more demanding: it had to have a range of {{convert|7,000|mi|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 {{convert|40|ft|m|abbr=on}} 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 {{convert|2,000|ft|m|abbr=on}} 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 {{convert|100|ft|m|abbr=on}} high was never solved.<ref name="brown" />