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.
Nuclear testing at Bikini Atoll
The second series of tests in 1954 was codenamed Operation Castle. The first detonation, Castle Bravo, was a new design utilizing a dry fuel thermonuclear hydrogen bomb. It was detonated at dawn on March 1, 1954. Scientists miscalculated and the 15 megaton (Mt) nuclear explosion far exceeded the expected yield of 4 to 8 Mt (6 Mt predicted), and was about 1,000 times more powerful than each of the atomic bombs dropped on Hiroshima and Nagasaki during World War II. The scientists and military authorities were shocked by the size of the explosion and many of the instruments they had put in place to evaluate the effectiveness of the device were destroyed.