The issue with current penetrators is they aren't designed for the mission. Reusing old designs but now with better guidance systems is really designing a new weapon system based on older principles which means a full R&D cycle and hoping people haven't built defenses for such an old approach.

There are three basic angles of attack, from the front, top, and water. Anything that comes in from the front or top and then detonates has a large hole to let energy back out without damaging the structure. The same issue also applies to a water entry with current perpetrators as these things are designed for high speed impacts which creates a large void behind the bomb.

Ideally you want something that lands in exactly the right spot and then slowly sinks to the right depth. And of course no netting to be around the dam to make the mission that much more difficult. Which gets back to my previous point, it’s clearly possible, just technically difficult.