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.
Operation Castle
As "Operation Castle" progressed, the increased yields and fallout caused test locations to be reevaluated. While the majority of the tests were planned for barges near the sand spit of Iroij, some were moved to the craters of "Bravo" and "Union". In addition, "Castle Nectar" was moved from Bikini Atoll to the crater of "Ivy Mike" at Eniwetok for expediency, since Bikini was still heavily contaminated from the previous tests.