The New Zealand Herald, citing the files, said that senior United States defence officials believed the weapon had the potential to be as deadly as the atomic bomb. But the tsunami bomb, as it was known, was never fully tested and the war ended before the project was completed.

Its mastermind was Thomas Leech, an Australian professor who as the dean of engineering at Auckland University from 1940 to 1950. He was seconded to the New Zealand Army during the Second World War. He set off a series of underwater explosions that triggered mini tidal waves at Whangaparaoa, just north of Auckland, in 1944 and 1945.

Details of the research, known as Project Seal, are contained in 53- year-old documents released by the New Zealand Ministry of Foreign Affairs and Trade.

The papers, stamped "Top Secret", show that America and Britain were keen for Seal to be developed in the postwar years. They even considered sending Professor Leech to Bikini Atoll to watch the US nuclear tests and see if they had any application to his work.

In the end, he did not make the visit, although Dr Karl Compton, a member of the US board of assessors of nuclear tests, was sent to New Zealand to meet him.

In July 1946, a letter from Washington to Wellington Defence Headquarters stated: "Dr Compton is impressed with Professor Leech's deductions on the Seal Project and is prepared to recommend to the Joint Chiefs of Staff that all technical data from the test, relevant to the Seal Project, should be made available to the New Zealand government for further study."

The announcement in 1947 that he had been awarded a CBE for weapons research led to speculation in some newspapers outside New Zealand about the nature of the work that he had been conducting. No details were released about it at the time because the project was still under way.

Neil Kirton, a former colleague of Professor Leech, told the New Zealand Herald that the experiments involved laying a pattern of explosives underwater to create a tidal wave.

Small-scale explosions were set off in the Pacific and off Whangaparaoa, which was controlled by the army at the time. Mr Kirton said he doubted whether people living in Auckland at the time would have noticed the trials.

What happened to Project Seal once the final report was forwarded to Wellington in the late 1940s is not clear.

Mr Kirton said: "If it could ever be resurrected, under some circumstances I think it could be devastating."