Project Habakkuk was a plan in WW2 to create a giant aircraft carrier made of ice. The British government wanted a better way of battling German U-boats.
Inventor Geoffrey Pyke came up with the idea of using solid blocks of ice, strengthened with sawdust, to create a ship big enough for bombers to land on.
Mega Builds is a video series from BBC Future looking at giants of engineering from around the globe.
Video script: Ed Barrett