Pert builds nukes

‘There are other elements that can be made into even mightier weapons,’ he said after a pause. Perturabo measured his words carefully, unsure of how much to reveal. ‘Elements with a certain quality of fissility. Rare elements. The ancients stripped this planet of most of its resources. They were disproportionately interested in fissile elements. If I can acquire enough, I will build a weapon of such awful potency that it will end war on Olympia forever.’
...
	Blazing spears of light stabbed down from the ships in orbit. Lance strikes ionised the atmosphere and sent thunderclaps of heat-shocked air across the mountains. They slammed into the near invisible void bubble covering Kardis. Unearthly growling echoed from the faces of Olympia’s stern mountains as it collapsed. The shrieking whine of incoming heavy ordnance made conversation impossible. Giant shells fell from the sky, burning white with the heat of re-entry. They left smoking contrails that crossed one another in gentle curves, and then, in a fury of fire and roaring destruction, they levelled Kardis. The sky blazed. The emissaries threw up their hands against the light and cried out.

An atomic bloom billowed from the city. Wind howled outwards, blowing the tent away and battering the emissaries down to their knees. Fire blasted out in every direction, setting the forests of the mountains alight and turning farmland in the valleys to poison ash. ‘I fought long and hard to find enough fissile elements to make the weapons that originally brought this world to its senses,’ shouted Perturabo over the moaning, hot death-wind blowing from Kardis. ‘Thanks to the Emperor and the priests of Mars, I have better weapons now, engines of destruction that you cannot imagine.’ The cap of the atomic cloud spread outwards, the pillar of steam and dust it rested on so thick it appeared solid. ‘You will not be given the chance to learn.’

Perturabo: Hammer of Olympia