HMS Habbakuk was a secret project undertaken by the British during WWII in order to better combat the German U-Boats in the Atlantic campaign. HMS Habbakuk was the brain child of Geoffrey Pyke who proposed the mixture of wood chips and water to make a very strong ice substance that became known as "Pykrete".
A scale model was built for project Habbakuk in the Canadian Rockies at Patricia Lake. In order to keep the project a secret, the scale vessel was built to resemble a 30' x 60' barn. The barn was built from wood and then covered in asphalt. The interior walls were all covered with ice blocks and the entire structure was kept chilled with a one horsepower motor operating a refrigeration unit.
There were three concept designs proposed for a full scale ship, but the logistics and materials required proved to be prohibitive as the vessel would cost more and use just as much structural steel as a traditional vessel, and the amount of pulp needed to make the needed pykrete would have a significant impact on the paper industry. The United States took control of the project from the British and the Canadians, and slowly let the project slip away after assessing its viability. The engineering efforts that were directed on this project were eventually reallocated to the Manhattan Project, and the scale models refrigeration system was turned off. The vessel melted and sunk to the bottom of Patricia Lake, where it still sits today.