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.
Rongelap Atoll
From 1946 through 1958 the United States military conducted numerous atmospheric nuclear weapons tests, including hydrogen bomb tests, primarily at Bikini Atoll, about from Rongelap Atoll. On March 1, 1954, the testing of the Castle Bravo hydrogen device produced an explosion that was 2½ times more powerful than predicted, and produced unexpected amounts of fallout that resulted in widespread radioactive contamination. The blast cloud contaminated more than of the surrounding Pacific Ocean including some of the then inhabited surrounding islands including Rongerik Atoll, Rongelap Atoll ( away) and Utirik Atoll.