Britain was taking a beating from the German ships and submarines and were looking for something to build a ship out of that couldn’t be destroyed by torpedoes, or at least could take a major pounding without incurring a fatal amount of damage. With steel and aluminum in short supply, Allied scientists and engineers were encouraged to come up with alternative materials and weapons.
One of [scientist Geoffrey Pyke’s] ideas was to build a 2,000 foot long, 300 foot wide and two million ton carrier. Besides the ship’s size, what was so different about Pyke’s vessel was that it would be built of ice.
There is no real limit on the availability of ice; it’s easy to make, fairly durable (except in warm temperatures), buoyant, and very easy to repair when damaged. Further, repairs can be made extremely quickly with the right equipment, even during a battle.
A dome made of the same substance – 96% ice, 4% sawdust.
Early experiments ran into problems, with the ice actually being too fragile to take much of a pounding, and the idea was shelved. Later that year, a firm from New York tried adding 4% sawdust and wood chips, and it worked much, much better – slower to melt, more buoyant, and stronger.
So what was the catch? To keep it from warping, the ship’s surface had to be covered in insulation and carry a refrigeration plant and system of ducts – actually not as crazy as it sounds, and a small scale version was built that worked perfectly well even in summer temperatures.
Better still, ballistic tests showed that it was very resistant even to direct torpedo hits. The ship would need a monster of a rudder, and its top speed was very slow, even for the time, so given the experimental nature of it the plan was ultimately scrapped.
As a footnote, the smaller test vessel took three summers to completely melt it.
Via Today I Found Out and Wikipedia.