During World War II we were going to build unsinkable aircraft carriers out of a mix of ice and wood shavings called Pykrete.
From wikipedia:
"Habakkuk II was closest to the COHQ model and would have been a very large, slow, self-propelled vessel made of pykrete with steel reinforcement. The size would have been a length of 1200 meters and a width of 180 meters"
For a comparison the Lexington-class aircraft carrier was 270 meters long 33 meter beam.