Believe it or not: During World War II, the British seriously considered building extra aircraft carriers with the hulls largely consisting of "pykrete" (a mixture of water and wood pulp, frozen into slabs, stronger than regular ice, and taking longer to melt) in order to conserve thousands of tons of steel for other purposes during wartime rationing. Of course, you would need a big refrigeration system onboard so that your ship didn't just literally melt away on a warm day. The research project was called "Project Habakkuk," but it never quite worked out. The concept stuck in my head and inspired this fictional "pure ice" version of an aircraft carrier.