Board Thread:Warhammer 40k General Discussion/@comment-96.237.238.119-20131218020230/@comment-72.49.66.138-20140112183854

They have indeed, once on Kronus and once during an attack by Tyranids on a slumbering Necrontyr refuge colonized by Tau. The Ethereal of the second world offered them peace and they responded with an atomic weapon that wiped the colony COMPLETELY. Everyone knows what happened on Kronus.