In September 1942, Geoffrey Pyke — an unpaid advisor to Louis Mountbatten's Combined Operations — walked into Mountbatten's office with a memorandum. The Atlantic mid-ocean air gap was killing convoys; U-boats sank ships beyond the reach of land-based patrol aircraft. Pyke's solution: build aircraft carriers out of ice. Not small ones — carriers 2,000 feet long, 300 feet wide, displacing 2 million tons, with 40-foot-thick hulls, immune to torpedoes because the damage would refreeze.

Mountbatten took the memo, walked to Chequers, and dropped a chunk of ice into Churchill's bath. The Prime Minister approved the project the same day. It was code-named Habakkuk, after the prophet: "Behold ye among the heathen, and regard, and wonder marvellously: for I will work a work in your days, which ye will not believe, though it be told you."

Pure ice fails under stress — it creeps and shatters. Max Perutz (later a Nobel laureate for hemoglobin structure) discovered that adding 14% wood pulp by weight produced a composite — pykrete — with the tensile strength of concrete, that melted 60% slower than pure ice, and that could be machined on a lathe. In Smithfield Meat Market, Perutz ran ballistic tests in a refrigerated chamber, firing rifles at pykrete blocks. Bullets bounced.

In winter 1943, at Patricia Lake in Jasper, Alberta, a 60-foot, 1,000-ton prototype was built by Canadian conscientious objectors who weren't told what they were making. It had a 1-hp refrigeration unit, wood-clad walls, and survived that summer. The full design called for 26 generator stations circulating brine through hollow cavities in the hull, 200 aircraft in an internal hangar, and a top speed of 7 knots on 33,000-hp electric motors.

Then it collapsed. Costs ran from £750,000 to £2.5 million per ship. Steel shortages eased. Long-range B-24 Liberators with drop tanks closed the air gap. The Azores opened to Allied bases. By December 1943, Habakkuk was quietly abandoned. The Patricia Lake prototype's refrigeration was shut off. It took three summers to melt. The engine block still sits on the lake bottom.

Here's the case for now:

• Pykrete 2.0. Modern composites — cellulose nanofibers, aramid pulp, basalt fiber, even graphene oxide — produce ice composites with 3–5× the tensile strength Perutz measured, at similar cost. Cambridge and Eindhoven have published on reinforced ice structures since 2015.
• Refrigeration is trivial. The 1943 design demanded 33,000 continuous horsepower for cooling. Modern absorption chillers driven by floating solar arrays — in polar summer, sunlight is 24 hours a day — make the energy budget close to zero.
• The Arctic is opening. As sea ice retreats, the Northern Sea Route needs infrastructure: search-and-rescue bases, deep-water science platforms, emergency refueling stations, disaster-response hospitals. Steel platforms cost billions and rust. A pykrete platform can be grown in place using local seawater and imported pulp barges.
• Iceberg towing is a solved problem. Since the 1970s, Newfoundland oil platforms have routinely towed million-ton icebergs out of their path. The naval architecture already exists.
• Repair is free. Damage refreezes. Try that with a steel hull.

The counter to Habakkuk was that the specific problem — the Atlantic air gap — got solved cheaper by other means. That was 1943's answer. In 2026, the problems are different: Arctic sovereignty, climate refugia, floating renewable megastructures. Perutz's material is still sitting in the lake, waiting.