Top-secret wartime experiments were conducted off the coast of Auckland to perfect a tidal wave bomb, declassified files reveal.
An Auckland University professor seconded to the Army set off a series of underwater explosions triggering mini-tidal waves at Whangaparaoa in 1944 and 1945.
Professor Thomas Leech's work was considered so significant that United States defence chiefs said that if the project had been completed before the end of the war it could have played a role as effective as that of the atom bomb.
Details of the tsunami bomb, known as Project Seal, are contained in 53-year-old documents released by the Ministry of Foreign Affairs and Trade.
Meanwhile, lagoon water rushing back into the space vacated by the rising gas bubble started a tsunami-like water wave which lifted the ships as it passed under them. At 11 seconds after detonation, the first wave was 1,000 feet (305 m) from surface zero and 94 feet high. By the time it reached the Bikini Island beach, 3.5 miles (6 km) away, it was a nine-wave set with shore breakers up to 15 feet (5 m) high, which tossed landing craft onto the beach and filled them with sand.