Project Habakkuk

Podcast Transcript

During the Second World War, the Allies were desperate to develop ideas to help them win.

Some of these ideas, such as the atomic bomb and the Norden bombsight, were so promising that they warranted investments of staggering amounts, reaching into the millions and billions of dollars.

Other ideas, such as training bats to drop bombs or pigeon-guided missiles, were so outlandish that they were never seriously considered.

However, there was one idea that seemed crazy, but it actually got attention at the highest levels of government.

Learn more about Project Habakkuk and the idea of making an aircraft carrier out of ice on this episode of Everything Everywhere Daily.

The difference between a crazy idea and a brilliant one is just a matter of perspective.

Many new ideas seem crazy at first, but once people warm up to the idea and give it some thought, crazy can become brilliant.

This episode is about an idea which at first seems crazy. However, the science behind it is actually sound, and the principles behind it are so easy to demonstrate that you could do it in your own house.

The idea in question began as a solution to a problem: the attacks on Allied shipping in the North Atlantic.

Shipping between the United States and the United Kingdom was a lifeline for the British during the war. American supplies, both civilian and military, made their way over the Atlantic by ship.

The German Kriegsmarine prioritized disrupting these ships, and its primary weapon was the U-boat.

The U-boats were devastating to Allied shipping. Between 1939 and 1945, approximately 3,500 Allied merchant ships were sunk by German forces in the Atlantic. This resulted in the loss of about 14.5 million tons of shipping.

It is estimated that around 72,000 sailors and merchant mariners from various Allied nations lost their lives in the Atlantic due to German attacks.

However, U-boats had a weakness. They were vulnerable to attack by aircraft. To attack a ship by torpedo, they had to be at periscope depth, and because they were powered by diesel engines, they couldn’t be submerged for extended periods of time.

If they were spotted by an airplane, there was little they could do except dive, that is assuming they even saw the airplane in the first place.

The solution to this, you might think, would be to put an aircraft carrier in the flotilla of ships going across the Atlantic. The problem with that is that aircraft carriers would then become the number one target of U-boats, and aircraft carriers are much more expensive than U-boats.

So, the problem was, how can you get aircraft into the middle of the North Atlantic Ocean without the ship they were on being sunk by the swarm of U-boats in the area?

One man had an idea…..

The idea came from the eccentric British inventor Geoffrey Pyke, who had worked on other unconventional war-related concepts. Pyke suggested that massive floating platforms made from ice could serve as unsinkable aircraft carriers.

Again, the idea wasn’t totally crazy. There are icebergs that float around the North Atlantic all the time. Perhaps you could break off a large ice flow from the Arctic, flatten the top so planes can land on it, and push it into the North Atlantic.

The best part is you can’t sink an iceberg.

Pyke dubbed this Project Habakkuk, named after a prophet from the Old Testament. Why it was named after Habakkuk was never really explained.

This isn’t just an opinion, either. After the sinking of the Titanic in 1912, a group known as the International Ice Patrol attempted to sink icebergs with bombs and torpedoes, and they did nothing.

Upon further review, the idea just wasn’t feasible. If you have ever had the chance to see an iceberg in person, you might have seen that they are highly irregularly shaped. Moreover, they melt, and eventually, they will flip over as they become imbalanced.

After the iceberg idea was nixed, Pyke had an idea.

He worked for the British War Office’s Combined Operations Group, a unit tasked with devising unconventional solutions to wartime problems. Pyke told his colleague Max Perutz, who would later win the Nobel Prize in Chemistry, about a paper he had read about how plastics could be made stronger by imbuing them with fibers like cellulose.

He wondered if they couldn’t do the same thing by putting fibers in water and then freezing it.

They tested it out, and the results were……astonishing.

By using as little as 4% of the water’s weight in sawdust, it made the ice as strong as concrete, weight for weight.

They ultimately found an optimal ratio of 85% water and 14% wood pulp by weight.

They performed a test where they fired a bullet at a block of ice, and it shattered.

They performed a similar test with a block of wood pulp-reinforced ice, which stopped the bullet. The bullet made a small dent and embedded in the block.

They had seemingly made a miracle substance out of the simplest ingredients.

They dubbed the new material pykrete, a portmanteau of Pyke, the person who came up with the idea, and “krete” from concrete.

The reason why the events I’m going to describe in this episode were taken seriously is because pykrete is a real thing.

If you are so inclined, you can actually do some of this yourself and test it. It is incredibly easy.

Put some water in a cup and freeze it. After a few hours, take the ice out and hit it with a hammer. It should break.

Now try the same thing, but in the water put some fibrous material. If you don’t happen to have any sawdust, you can use cotton balls or even shredded-up newspapers.

Freeze it and then hit it with a hammer. You’ll find that it doesn’t break.

So why does adding wood to ice turn it into a totally different substance?

The wood fibers act like a reinforcing mesh within the ice. When the ice undergoes stress, instead of cracking or shattering, the wood fibers help to hold it together, much like how steel rebar strengthens concrete. This greatly increases the material’s tensile strength.

Unlike pure ice, which can be brittle, Pykrete is more flexible under certain conditions. The wood fibers allow the material to bend slightly without breaking, making it more resilient to impacts or stresses from expansion and contraction.

Furthermore, the wood pulp in Pykrete also helps insulate the ice, slowing down the rate at which it melts. As we can see, this actually became a very important property.

The biggest thing, however, is that the materials to make pykrete were cheap. For a country suffering from wartime shortages, the idea that such a strong building material could be made from water and wood was extremely appealing.

Pyke proposed that if they couldn’t build Project Habakkuk out of an iceberg, they could build it out of Pykrete.

Pyke proposed a gigantic aircraft carrier made out of pykrete. When I say giant, I mean something far larger than any aircraft carrier or ship evermade before or since.

The proposed vessel would have a length of 2,000 feet or 610 meters, a width of 300 feet or 91 meters.

The deck of the ship would have an area of about 6 acres or 2.4 hectares, and the total weight would be around 2 million tons.

Now, at this point, you might be thinking that even if pykrete is everything I described, there is still the small problem of the ice melting once it was at sea.

To counter this, it would be equipped with refrigeration units to keep the Pykrete from melting, in addition to propulsion systems for movement and enough anti-aircraft guns to defend itself against enemy bombers.

In September 1942, Pyke sent a 232-page memorandum to Lord Louis Mountbatten, who had taken over the Combined Operations Group.

His report outlined a plan for building the ship as well as for how it would aid in the battle of the North Atlantic and possibly assist in a future invasion of mainland Europe.

Lord Mountbatten became a supporter of the idea.

In early 1943, they conducted a test of pykrete on Lake Patricia in Jasper National Park in Alberta, Canada. They built a prototype ship that was 60 feet or 18 meters long and weighed 1,000 tons.

It had walls made of wood and tar with refrigeration pipes in the walls of the ship.

The refrigeration unit supposedly still sits at the bottom of Lake Patricia.

It should be noted that once the test was over, the test craft melted for three entire summers.

There is a legend regarding how pykrete was presented to President Franklin Roosevelt and Winston Churchill.

The famous incident took place in 1943 during a top-level Allied meeting in Quebec, Canada, where Lord Mountbatten was asked to explain the potential of Pykrete to both Churchill and FDR. Mountbatten, known for his dramatic flair, decided to use an unconventional method to demonstrate the strength of Pykrete compared to regular ice.

To highlight Pykrete’s durability, Mountbatten brought two blocks to the meeting: one made of ordinary ice and one made of Pykrete. He wanted to show that while ice is brittle and easily shattered, Pykrete was much stronger and resistant to breaking.

Mountbatten first invited them to observe the properties of the materials. Then, in a bold move, he took out a revolver and, with everyone watching, he shot at the block of ordinary ice. As expected, the ice shattered easily. Next, he fired at the block of Pykrete. Instead of shattering, the bullet ricocheted off the Pykrete block, reportedly grazing the leg of an admiral in attendance.

Both Churchill and FDR were impressed by the material, however, after further study, Project Habakkuk was deemed to be impractical.

By late 1943, the complexity of constructing a Pykrete vessel, combined with technological advances in aircraft and long-range bombers, made the idea unnecessary.

Long-range bombers, like the Consolidated B-24 Liberator, began to solve the problem of the Atlantic Gap. These new aircraft could patrol longer distances, making the need for a massive ice carrier less critical.

The scale of the project was immense, and it became clear that building even one of these massive carriers would require an enormous amount of resources, including refrigeration units, wood pulp, and manpower.

Building the ship, especially during wartime, presented huge logistical challenges. The material, though strong, still required constant refrigeration to maintain its integrity, especially in warmer waters.

While Project Habakkuk never came to fruition, there was still pykrete. What happened to it?

Researchers and engineers have sporadically revisited Pykrete as a curiosity. Its unique properties—such as the way wood fibers reinforce the ice—continue to intrigue materials scientists. However, no practical large-scale uses for Pykrete have been found in the decades since.

Several universities in Europe have experimented with creating pykrete domes in the winter by spraying a water and wood pulp mixture onto an inflatable dome.

There were also some who have suggested it would make for an excellent building material in space, assuming, of course, we could find water in space and put enough wood pulp into orbit.

Pykrete has remained an interesting substance with no real application. While its component materials are cheap, working with ice and keeping it frozen has proven too difficult to work with.

That is why, despite having piqued the interest of leaders on both sides of the Atlantic, Project Habakkuk never went beyond the design stage.