Lithium hydride
Before the Castle Bravo nuclear weapons test in 1954, it was thought that only the less common isotope lithium-6 would breed tritium when struck with fast neutrons. The Castle Bravo test showed (accidentally) that the more plentiful lithium-7 also does so under extreme conditions, albeit by an endothermic reaction.
Castle Romeo
Like the Ivy Mike and Castle Bravo tests, a large percentage of the yield was produced by fast fission of the natural uranium "tamper"; 7 megatons of the yield were from this source.