KenV,
Highball was anti-shipping. A smaller ball shaped bomb carried in the UK by the Mosquito.
Same basic principle of a spinning bomb as for the dams, to drive itself downwards, but in the case of Highball it was designed to rotate down to the keel and, on the fuse detecting it had reached the bottom and descent had stopped, to detonate and act in the same way as a torpedo - blast to lift the hull and create a void so that the ship would break its back as it came down again with only support at the bow and stern.