As 1942 began, the Americans had joined World War II and the Battle of the Atlantic began to intensify. German U-boats were picking off merchant ships at an alarming rate. From January 13 to February 6, Hitler's wolfpacks dropped 157,000 tonnes of Allied shipping to the bottom of the ocean — and without incurring a single loss. Later that October, 56 ships totalling 258,000 tonnes were sunk in the "air gap" between Greenland and Iceland.


And therein laid the problem: The mid-Atlantic was inaccessible to submarine snuffing Allied aircraft. It was a desperate situation that called for a radical solution. Looking to turn things around, Winston Churchill — an ardent supporter of unique technological innovations — approved Operation Habakkuk: The plan to create a fleet of massive aircraft carriers made from ice.

Above image: An idealized artistic impression of the H.M.S. Habakkuk.

Indeed, Churchill was in no mood to see the war in the Atlantic slip even further out of control. Throughout its history, the island nation had recognized the importance of sea power, and World War II was proving no different.


Britain required more than a million tons of imported material each week in order to be able to survive and fight the Germans. But by that stage in the war, the country's inhabitants were already on food rations. Churchill was genuinely concerned that mass starvations were right around the corner. Moreover, if a second European front was ever going to happen, the sea lanes had to be free from marauding U-boats.

Churchill later wrote, "The Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea or in the air depended ultimately on its outcome." After the war, he admitted that U-boats were the only thing that truly terrified him during the struggle.

Thus, to Churchill's surprise, a potential solution came in the form a unique material consisting primarily of ice. While taking a bath one day at his home at Chequers in late 1942, an excited Lord Louis Mountbatten — the British military Chief of Combined Operations — stormed in and dropped a chunk of ice between Churchill's legs. During the course of the next several minutes, the two watched in amazement as the ice refused to melt in the warm water.


A frozen slurry of wood pulp and ice

It was called pykrete, the invention of Geoffrey Pyke, an eccentric scientist who was working for Combined Operations. Earlier that year, Pyke was struck with the idea of creating floating islands made from carefully sculpted icebergs. He eventually realized, however, that his vision was unworkable. Standard ice was simply too weak. He needed something considerably more durable.


No doubt, ice is not a great material to work with. Under normal conditions, ice that has been moulded into a beam will fracture at loads anywhere from five kilograms per square centimeter (70 pounds per square inch) to 35 kilograms per square centimeter (500 pounds per square inch). Moreover, because it fails at unpredictable loads, it's not an ideal medium for construction.


Undaunted, Pyke figured he could find a way to reinforce ice, so he began to experiment with various concoctions. After a process of trial-and-error, he threw some wood pulp into the mix — and the ensuing difference in strength was dramatic. The new material, dubbed pykrete, increased the strength of regular ice to 70 kilograms per square centimeter (1,000 pounds per square inch) — enough to deflect a bullet shot at close range (as proven later in this story). It also had tremendous crush resistance; a one-inch column would be able to support an entire automobile. Further, pykrete took a lot longer to melt than regular ice.


Pyke had stumbled upon a rather fortuitous combination of materials. When water freezes, the hydrogen and oxygen atoms form a six-sided crystalline structure. These crystals provide open spaces, which is why water expands as it freezes, and why it's susceptible to pressure changes. Pykrete, on the other hand, still takes advantage of the crystalline structure, but the cellulose fibres from the wood pulp reinforces it in a way that's similar to how concrete is reinforced by steel wiring. Once frozen, it's about 14 times stronger than regular ice, and tougher than concrete.

A work in your days which ye will not believe

This was the wonder material that Pyke was looking for — what would form the basic building block of his giant floating island made from ice. He presented his findings to Mountbatten, who in turn brought the plan to Churchill's attention.


And for good reason; Churchill displayed a tremendous willingness to entertain unconventional ideas. Indeed, during the course of the war the Allies employed unorthodox tactics like dropping streams of tinfoil from planes to confuse enemy radar (dubbed "Window" — and an idea the Nazis later stole when bombing London in 1944), the development of miniature submarines, the construction of artificial harbors (called mulberries — an idea that Churchill first sketched out in 1917!), and dam busting bouncing bombs.

Pykrete, thought Mountbatten, could be another unconventional innovation. He told Churchill that it would last indefinitely and be self-healing against bullets, bombs and torpedoes. Ice was inherently unsinkable, and any holes could quickly be patched up with quickly freezing water. The ice-carriers would also reduce Britain's dependency on steel.


Churchill, who used to worked for the First Lord of the Admiralty and was an inventor in his own right, immediately seized upon the idea.

"I attach the greatest importance to the prompt examination of these ideas," he wrote in his ensuing approval letter. "The advantages of a floating island or islands, even if only used as refueling depots for aircraft, are so dazzling that they do not need at the moment to be discussed." He stamped the letter ‘Action This Day.'


Operation Habakkuk was officially underway. Churchill, though not a religious man, came up with the name by referring to an old Testament text which read, "Behold ye among the heathen…for I will work a work in your days…which ye will not believe."


Once developed, Churchill planned to deploy the ice-carriers off the coast of France and in the Indian Ocean where they would primarily serve as refuelling stations for the RAF. The plans called for an entire fleet, with each carrier measuring 2,000 feet long, 300 feet wide, and with walls forty feet thick. The entire structure would displace two million tonnes of water and be stitched together using 40 foot blocks of pykrete. Had it been constructed, it would have been the largest floating structure ever built.

Each carrier would be capable of carrying over 300 aircraft of all sorts, including bombers and fighters (like Spitfires and Hurricanes, which did not have folding wings). For contrast today's Nimitz class carriers can carry 90 aircraft. On the downside, however, the designs called for a structure that could only travel at 6 knots (11 km/h or 7 mph).


Eventually, Churchill shared the plan with his American allies, who exhibited more skepticism than they did enthusiasm.

After a heated discussion among the Allied chiefs of staff at Quebec's Chateau Frontenac Hotel in August 1943 on another matter, Mountbatten suddenly announced that he was going to give a demonstration. He pulled out two blocks of ice: a regular chunk of ice, the other pykrete. Without warning, he pulled out his revolver and shot the ice block, shattering it to pieces. Then he turned the gun to the pykrete and pulled the trigger. The bullet ricocheted off the block and buzzed around the room like an angry bee. The bullet grazed the legs of U.S. Fleet Admiral Ernest King and U.K. RAF Marshal Charles Portal, shocking the Allied chiefs — who soon erupted into a chorus of relieved laughter. Meanwhile, outside the room, a junior officer was heard to exclaim, "Good God, they've started shooting now!"


This bizarre episode aside, some members of the Combined staff were intrigued by what the ice islands could mean for the war in the Pacific theatre. In one scenario, fleets of ice-aircraft carriers could be brought down from the Aleutian Islands and re-located near the Japanese main island. From there, squadrons of B17 or B29 bombers could be deployed — and all without having to displace Japanese troops from the surrounding occupied islands.

Building the behemoth

The first stage of Habakkuk involved some proof-of-concept testing. Along with the Austrian-born British molecular biologist, Max Perutz, Pyke set to work on refining the material in an ultra secret location in Great Britain: a refrigerated meat locker in a Smithfield Market butcher's basement. The team's "assistants" were British commandos in disguise, and they worked behind a protective screen of frozen animal carcasses. Even Mountbatten came to visit one day, but had to be disguised as an everyday civilian.


Once satisfied with their mixture — 86% ice and 14% wood pulp — the project was relocated to Patricia Lake in Jasper, Canada, where a scale model was built in the summer of 1943. The location was chosen on account of its remoteness, frigid climate, and accessibility to crucial railway lines.

To construct the miniature prototype, a team of "alternative workers" was employed — a group of conscientious objectors who hadn't the slightest clue what they were building.


The scale model measured 60 feet long and 30 feet wide. It weighed 1,000 tons, and was kept frozen by a 1-horsepower motor.


And indeed, it soon became obvious that pykrete was not immune to the elements — it was in fact susceptible to melting. To deal with this, the designers had to provision for a complex cooling system — which essentially turned the H.M.S. Habakkuk into a giant refrigerator. The entire structure would have be fitted with a series of pipes that ran coolant. Suddenly, the project became considerably more complicated — and an order of magnitude more expensive.

Moreover, the amount of material required to build just one Habakkuk was immense. Hundreds of thousands of tons of wood pulp would be required — an amount that would have a profound impact on the production of other wood and pulp based products, including (and especially) paper.


It also became obvious that the Americans would have to get involved by providing the large quantities of steel required.

The project started to spiral out of control on account of untenable technological hurdles, supply problems, and rapidly escalating costs. Churchill himself got cold feet when he learned that each carrier would cost upwards of £6 million.


Died on the vine

Though the scale model was built, the project was eventually cancelled.

By the time the developers were ready to go with the full-blown version — which was now 1944 — the situation in the war was dramatically different. The Battle of the Atlantic had been won, and the Americans were mass producing small aircraft carriers at a daunting rate. In addition, Portugal made its airfields available to the Allies, land-based aircraft were attaining longer ranges, and U-boats were being sunk at rates faster than they could be built. Moreover, the U.S. was making progress in the Pacific without the floating islands. And of course, there was always the chance the the atomic bomb would soon end things once and for all.


So, with Operation Habakkuk canceled, the model sat abandoned on the surface of Patricia Lake — where it didn't melt until later the following summer. In the 1970s, remnants of the prototype were found and studied. Today, a plaque commemorating Operation Habakkuk can be seen on the lake's shore.

Sources: The Last Lion: Winston Spencer Churchill: Defender of the Realm, 1940-1965 (Manchester & Reid), London Evening Standard (1951), Cabinet Magazine, Royal Naval Museum.


Images: Library of Congress, UAF, Irrational Geographic, BookOfNorm.