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 Yankee
It was detonated on May 5, 1954, at Bikini Atoll of the Marshall Islands, on a barge moored in the middle of the crater from the Castle Union test.