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 Bravo
The Shrimp device design later evolved into the Mark 21 nuclear bomb, of which 275 units were produced, weighing and measuring long and in diameter. This 4-megaton bomb was produced until July 1956. In 1957, it was converted into the Mark 36 nuclear bomb and entered into production again.