In late 1942, Lord Louis Mountbatten—the British military’s Chief of Combined Operations—paid a visit to Winston Churchill at his official country home, Chequers. Mountbatten had with him a small parcel of great importance. A member of Churchill’s staff apologized that the Prime Minister was at that moment in his bath.

“Good,” said Mountbatten as he bounded up the stairs. “That’s exactly where I want him to be.” Mountbatten entered the steaming bathroom to find Churchill in the tub. It was generally not a wise thing to interrupt Sir Winston in his bathtub.

“I have,” Mountbatten explained, “a block of a new material that I would like to put in your bath.”

Mountbatten opened his parcel and dropped its contents between the Prime Minister’s bare legs in the water. It was a chunk of ice.

Rather than bellow at his Chief of Combined Operations, Churchill stared at the ice intently—and so, standing by the bathtub, did Mountbatten himself. Minutes passed, and still they looked into the steaming depths of bath water before them. The ice was not melting.1

Ice is strange stuff: brittle when struck suddenly, yet malleable when pressured over a period of time. With low but steady pressure, this plastic deformation can continue indefinitely. Above all, ice is unpredictable. Molded into a beam, it will fracture at loads anywhere from five kilograms per square centimeter to thirty-five kilograms per square centimeter. Because it fails at unpredictable loads, it is not ideal as a building material. But what was bobbing about in Churchill’s bathtub was no ordinary ice: it was pykrete.

Pykrete is a super-ice, strengthened tremendously by mixing in wood pulp as it freezes. By freezing a slurry of 14 percent wood pulp, the mechanical strength of ice rockets up to a fairly consistent seventy kilograms per square centimeter. A 7.69 mm rifle bullet, when fired into pure ice, will penetrate to a depth of about thirty-six centimeters. Fired into pykrete, it will penetrate less than half as far—about the same distance as a bullet fired into brickwork. Yet you can mold pykrete into blocks from the simplest materials and then plane it, just like wood. And it has tremendous crush resistance: a one-inch column of the stuff will support an automobile. Moreover, it takes much longer to melt than pure ice. But as strong and eco-friendly as it is, pykrete remains forgotten today save among glaciologists, who express bafflement over why no one has made use of it. “I don’t really know why it has languished in obscurity,” admits Professor Erland Schulson, director of the Ice Research Laboratory at Dartmouth College.2

Pykrete is the namesake of Geoffrey Pyke, who the Times of London once declared “one of the most original if unrecognized figures of the present century.” His career began in 1914 when, as a teenager at Cambridge University, he landed a foreign correspondent job by using a false passport to sneak into wartime Germany. After getting tossed into a concentration camp, he fled the country in a daring daytime escape. In the 1920s, he virtually created progressive elementary education in Great Britain, all for the sake of his own son’s education. Pyke financed his own school by brilliantly riding futures markets and controlling a quarter of the world’s supply of tin, a ploy which brought him to financial ruin in 1929. He lived on as an eccentric hermit, publishing prescient warnings of Nazism and proposing one of the first media watchdogs. After the war, his freelance genius helped propel the creation of the National Health Service.3

During the war, he appeared at the office of the Chief of Combined Operations with a simple recommendation for his hiring. “You need me on your staff,” the shabbily dressed man explained to Lord Mountbatten, “because I’m a man who thinks.” What Pyke was thinking about just then was building ships out of ice.

Pyke envisioned ships as vast and solid as icebergs. You could make the sides of your boat tens of feet thick, hundreds if you felt like it, and bullets or torpedoes would bounce away or knock off pathetically ineffectual chunks. And when a torpedo did knock a chunk away—so? You were floating in a sea of raw repair material. Given how long it took pykrete to melt, and the minimal onboard refrigeration equipment needed to stay frozen and afloat, it would be months or years before the boats exhausted their usefulness. In battle, the ice ships could put their onboard refrigeration systems to good use by spraying super-cooled water at enemy ships, icing their hatches shut, clogging their guns, and freezing hapless sailors to death.

Pykrete freighters could carry eight entire Liberty class freighters as cargo, but Pyke’s dream was not to use them as cargo ships but as aircraft carriers. One of the great disadvantages of aircraft carriers had always been that their short landing surfaces and cramped storage favored small planes with foldable wings and light armor. The most desirable fighters, like Spitfires, were not an easy fit for carriers, and bombers were altogether out of the question. Pyke’s logical conclusion was to build a behemoth: the HMS Habbakuk, he called it. Constructed from forty-foot blocks of ice, his Habbakuk would be two thousand feet long, three hundred feet wide, with walls forty feet thick. Its interior would easily accommodate two hundred Spitfires. The largest ship then afloat was the HMS Queen Mary, which weighed in at eighty-six thousand tons. The Habbakuk would weigh two million tons.4

For a man who had had ice thrown into his bath, Winston Churchill was surprisingly receptive to the idea. After reading the formal War Cabinet report on the Habbakuk project, Churchill shot back a memo stamped “Most Secret” the next day, on 7 December 1942. “I attach the greatest importance to the prompt examination of these ideas,” he wrote. “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.”