Germany’s U-boats in World War II, it posed a huge problem for the British, who found themselves short on the resources needed for anti-submarine warfare. The treaty of Versailles that ended WWI forbid Germany from building new submarines, so why have destroyers and aircraft that could hunt submarines at all? A piece of paper had eliminated the U-boat threat to England in the future.

Well, the Germans just built U-boats without telling anyone about it.

The Problem

When war broke out about 100 U-boats scattered into the Atlantic almost like mobile and invisible landmines just waiting for a hapless merchant ship to stubble into them.  The Atlantic is immense and the Royal Navy did not have enough ships to hunt all these U-boats down and the U-boats were smart enough to position themselves out of the range of allied aircraft.   What if there was a way to extend their range with floating bases out in the Atlantic they could land and refuel on.  Not aircraft carriers, which the Royal Navy needed to protect its own surface ships at sea, and long-range bombers couldn’t possibly land on them but something else, like a huge barge. The war meant materials like wood, steel, paint, engines, and other supplies for making large ships were already spoken for.  Enter Geoffrey Pyke, who had an interesting idea: what if they made a huge aircraft carrier out of a unique mixture of wood, pulp, and ice? The idea was to be called “Project Habakkuk.”

Pike was a journalist, educationalist, and inventor.  He was already well known for escaping from an internment in Germany during World War I. He was recommended to the Chief of Combined Operations named Lord Mountbatten by cabinet minister Leopold Amery. So he worked for the Combined Operations Headquarters alongside his friend, J.D. Bernal, and was regarded as a genius.

Pyke’s Solution

Living up to his wonderboy reputation, and as Lord Zuckerman described him as “not a scientist, but a man of a vivid and uncontrollable imagination, and a totally uninhibited tongue,” he came up with the Habakkuk idea while he was organizing the production of M29 Weasels for Project Plough in the United States. Project Plough was a scheme to create an elite unit to be assigned in the winter operations in Norway, Romania, and the Italian Alps. How could they create a floating island base for aircraft and even flying boats to use in the mid-Atlantic while scouting for U-boats?

By making them out of Atlantic icebergs, of course.

You see, using ice would only require 1% of the energy that was usually needed to make the same mass using steel. So here’s his proposal: Get an iceberg, be it natural or artificial, and then level it so that planes could use t as a runway. Also, hollow it out so that it could shelter the aircraft.

A block of pykrete. (CyranoDeWikipediaCC BY-SA 3.0, via Wikimedia Commons)

He immediately sent the proposal through the diplomatic bag to the Combined Operations HQ while he was in New York. He made sure that nobody would know of his genius plan and labeled it so that only Mountbatten could open the package. In turn, Mountbatten passed Pyke’s proposal to Churchill, who was excited about the idea. “Genius!” he probably exclaimed.

On a side note, though, a German scientist named Dr. A Gerke had the same concept of the idea before, and he even carried out some preliminary experiments in 1930. However, he wasn’t taken seriously, and the idea was treated as a joke.

Turning It Into Reality

With the help of molecular biologist Max Perutz, they determined if it was possible to quickly build an ice floe large enough to withstand the Atlantic conditions. When Pertuz explained that natural icebergs are prone to rolling over and their surface area is too small, the government helped develop Pykrete, named after Pyke. It was a mixture of water and wood pulp that is stronger than plain ice when frozen. It also melts slower and it floats. Pykrete could be cast into shapes just like metal. Also, it forms an insulating shell of wet wood pulp when immersed in water, protecting its interior from melting.

Another problem: As per Perutz, ice flows slowly, known as plastic flow, and according to his tests, a pykrete ship would gradually sag unless cooled to 3 degrees Fahrenheit, insulation that would require the use of a huge refrigeration plant and a complicated system of cooling ducts.

Construction concept for an ice-based aircraft carrier. (99% Invisible)

Regardless, a large-scale model was soon ordered in Canada to test its possibility, both physically and financially. the Habakkuk model was built on the large-scale model of the Habbakuk built in Alberta was 18 by 9 meters (60 by 30 feet) and weighed 1,000 tons. The location of the experiment was Patricia Lake, near Jasper, Alberta, chosen for its seclusion, proximity to a railroad, and cold climate.  The mockup was made to look like a floating boat house to prevent prying eyes from figuring out what it really was(as if anyone could have).

Both Mountbatten and Churchill loved and supported the Habakkuk idea, but the National Research Council of Canada, who did the testing, determined that while feasible in testing, building a single Habakkuk would cost more money in terms of man-hours and machinery than a whole standard fleet of aircraft carriers might cost.


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Its specifications would have made it truly massive at 1.8 million tons of displacement and some 2,000 feet in length. It would dwarf a modern nuclear-powered carrier of the US Navy.  It would have had 14 propellers along its sides and dozens of cannons and anti-aircraft guns as well. Somehow, it would have a crew of nearly 3,5000 personnel and be able to take between 100-200 aircraft aboard.

In the end, the project was canceled, with the last meeting of the Habakkuk board being in December 1943.

Before you dismiss this whole thing as a waste of time and money in the early desperate days of WWII, you might first consider the fate of the prototype abandoned and forgotten on Patricia Lake.

It is reported that it took three full summers for it to melt and the pykrete to sink to the lake bottom. Given the relatively short lifespan of most aircraft carriers in the carnage of WWII, that was quite a record.