A new book about New Zealand's national archives says it holds details of a World War II plan to create a tsunami bomb.
Project Seal was a top-secret joint United States-New Zealand attempt to create a doomsday device to rival the nuclear bomb.
Secrets Treasures author Ray Waru said the project was launched in June 1944 after a US naval officer noticed that blasting operations around Pacific islands sometimes produced a large wave, raising the possibility of creating a "tsunami bomb".
Other notable documents held in the archive are a letter written by Captain James Cook before his final voyage.