When Paul Atreides and the Fremen attack Arrakeen, what is their most powerful weapon?

When Paul Atreides and the Fremen attack Arrakeen, their most powerful weapon is nuclear weapons. Paul uses the Atreides family atomics to destroy part of the Shield Wall, the natural rock fortification protecting Arrakeen from the desert.

The nuclear strike creates an opening for the Fremen assault. Paul’s forces then ride giant sandworms through the breach during an electrical storm. The storm shorts out the Sardaukar’s defensive shields, allowing the Fremen to overwhelm the imperial and Harkonnen forces inside the capital.

Paul carefully directs the atomics against the Shield Wall rather than directly against human targets. This distinction lets him claim that he has not violated the Great Convention’s prohibition on using atomics against people, even though the blast is strategically decisive.

Sandworm riders are an essential part of the attack, but they are not the most powerful weapon in the question’s sense. The atomics produce the breach that makes the final invasion possible and are therefore the correct answer.