New Details Emerge on World War II ‘Tsunami Bomb’ Project

Patrick Goodenough | January 3, 2013 | 5:00am EST
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A whirlpool caused by currents from a huge earthquake-generated tsunami swirls near the Japanese port of Oarai on March 11, 2011. (AP Photo)

( – The revelation that the United States and New Zealand carried out “tsunami bomb” tests during World War II, first made public 14 years ago when secret documents were declassified, is making headlines again after a researcher dug up more archived material.

Thousands of bombs were dropped and their effects monitored in tests around New Caledonia – then an important Allied base, now a special-status French territory – and near Auckland, New Zealand’s largest city.

The aim of the project, in the dry language of the archived documents, was “the investigation of the potentialities of inundation by means of artificially produced tidal waves for offensive purposes” – in other words, to see whether a bomb or series of bombs could generate a tsunami capable of wreaking havoc on an enemy coastal city.

Since the New Zealand government in 1999 declassified material relating to “Project Seal,” devastating tsunamis in the Indian Ocean in 2004 and Japan in 2011, both triggered by undersea earthquakes, underscored just how effective such a weapon could be in theory.

The archived documents detail the findings, as a team led by Thomas Leech, an Auckland University professor seconded to the army, carried out tests to find out what shape and size of bomb or series of bombs, detonated in water of what depth, would have the desired effect.

The idea first arose in early 1944 when a U.S. Navy officer, in a conversation with the commander-in-chief of the New Zealand Army, recalled that during earlier survey work in the Pacific he had sometimes observed unexpectedly large waves during the blasting of submerged coral reefs.

Early tests were promising enough for U.S. Navy South Pacific commander Admiral William Halsey to call for more, writing that the results, in his opinion, “show that inundation in amphibious warfare as definite and far-reaching possibilities as an offensive weapon.”

Single explosions were found to be “inefficient in the production of waves,” Leech reported in one of the archived papers.

However, “[t]he use of multiple charges located to conform with geometrical patterns was found to give markedly superior results,” he wrote, adding that factors including the shape of the charge, the spacing, and the location were all important, and that the best results occurred when explosions were adjacent to the water surface, rather than at greater depth.

Leech concluded that 2,000 tons of high explosive, divided into ten equal amounts and detonated as a group around five miles offshore in a location where the seabed was favorable, could potentially create a wave of 30 to 40 feet.

The papers do not name a target for the envisaged weapon, but when the New Zealand government first unlocked the files in 1999 an 87 year-old survivor of the team said it was obvious to those involved that the aim was “to flood Japan.”

The tests ended in early 1945, but there is evidence in the documents of ongoing interest after the war ended.

Leech was invited to observe atomic bomb trials in Bikini Atoll in 1946 and, although unable to do so he did provide the U.S. with data about placement of submerged explosives. (The second Bikini test involved an atomic bomb suspended 90 feet below the surface of the sea, testing its effect on Navy ships.)

That same year top American physicist Karl Compton, who served on a secret high-level group advising the U.S. government on the nuclear issue and was a member of the Naval Research Advisory Committee, visited New Zealand and examined the “Project Seal” findings.

Secret documents about the “tsunami bomb” tests were first declassified by New Zealand’s government in 1999. (Image: NZ Archives)

A letter from the U.S. to the New Zealand government after the visit said Compton was “impressed with Prof. Leech’s deductions on the Seal project” and recommended the release of technical data to enable Leech to carry out further study.

In 1950 secret reports were still being produced in New Zealand about the World War II experiments. Leech in one document discussed the possibility of having some of his top students work on filling in some of the gaps left in the earlier findings, under the cover of regular oceanography and wave studies.

The papers do not indicate whether that ever happened but Leech left the university that same year and returned to his native Australia. He  was awarded a CBE (Commander of the Order of the British Empire) for his secret research on a weapon, and died in 1973.

In 1961, the U.S. Navy motivated a request for the final “Project Seal” report to be downgraded from “secret” to “restricted” by arguing that the data would be “extremely helpful” in military studies being carried out.

“Project Seal” is back in the spotlight because of the release of Secrets and Treasures, a new book by New Zealand author Ray Waru, based on a two-year trawl though the New Zealand government archives.

The testing in New Zealand of a possible “tsunami bomb” coincided with top-secret work in the U.S. leading up to the first nuclear detonation test in New Mexico in July 1945, and the first use of an atomic bomb in Japan a month later.

Ironically, the two allies which had worked together on a potential non-nuclear weapon of mass destruction later had a serious disagreement over nuclear policy.

In the 1980s, a Labor government in New Zealand banning nuclear-armed and nuclear-powered ships from docking in its ports. The policy effectively ended New Zealand’s participation in the tripartite ANZUS defense pact – which continues as a bilateral U.S.-Australia alliance – and led to a downgrading in Wellington’s status from “ally” to “friend.”

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