Castle Bravo was a hydrogen bomb test by the americans during the cold war in bikin atoll and first of the operation castle nuclear tests.
Initially, the bomb, known as the 'shrimp' device was set to explode at 6000 kilotons, however it was unexpected that the bomb would explode at 15000 kilotons, which is more than twice as expected and also a thousand times more powerful than the bomb that exploded over hiroshima during world war II.
What makes this deadly is that there is a massive fallout that poisoned bikini atoll inhabitants and a japanese fishing boat, with the people afflicted by radiation sickness, and eventually leading to one of the japanese fisherman succumb to his illness.
This had caused widespread anger among the japanese as this is not the first time they had suffered a nuclear attack.
This event also lead to people creating a film called 'Godzilla', probably to protest against nuclear weapons testing.