The tests were carried out in waters around New Caledonia and Auckland during the Second World War and showed that the weapon was feasible and a series of 10 large offshore blasts could potentially create a 33-foot tsunami capable of inundating a small city.

The top secret operation, code-named “Project Seal”, tested the doomsday device as a possible rival to the nuclear bomb. About 3,700 bombs were exploded during the tests, first in New Caledonia and later at Whangaparaoa Peninsula, near Auckland.

The plans came to light during research by a New Zealand author and film-maker, Ray Waru, who examined military files buried in the national archives.

“Presumably if the atomic bomb had not worked as well as it did, we might have been tsunami-ing people,” said Mr Waru.

“It was absolutely astonishing. First that anyone would come up with the idea of developing a weapon of mass destruction based on a tsunami … and also that New Zealand seems to have successfully developed it to the degree that it might have worked.” The project was launched in June 1944 after a US naval officer, E A Gibson, noticed that blasting operations to clear coral reefs around Pacific islands sometimes produced a large wave, raising the possibility of creating a “tsunami bomb”.

“If you put it in a James Bond movie it would be viewed as fantasy but it was a real thing,” he said.

“I only came across it because they were still vetting the report, so there it was sitting on somebody’s desk [in the archives].”