Fantastically chronicled in Atoms and Ashes. [^1]
The explosion was so powerful that the personnel in the monitoring station who were not expected to receive any radiation at all had to hide in a back room of their concrete bunker and hope an evacuation was possible. The radiation & fallout was so intense that all the monitoring ships had to leave their assigned stations. The bomb was a full 2.5 times what the designers expected: 15 megatons as opposed to 6. Just a complete unnecessary tragedy for the islanders.