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 Union
The test took place on April 26, 1954 at Bikini atoll of the Marshall Islands, on a barge moored in the lagoon, off Yurochi island. The yield of 6.9 megatons of TNT was somewhat higher than the predicted 3-4 megatons. Although the barge had been moored in over of water, the test left a crater in diameter and deep in the bottom of the lagoon.