Extracted from Secrets & Treasures: Our stories told through the objects at Archives New Zealand by Ray Waru (Random House)

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Since the devastating tsunami wrought havoc across Indian Ocean in 2003, and another deadly wave killed thousands along the coast of Japan in 2011, the very thought of harnessing the destructive force of a tsunami as a weapon of war might be condemned as megalomania or simply dismissed as silly science fantasy.

But in 1944 that is exactly what scientists were trying to achieve off the Whangaparaoa Peninsula in the quiet upper reaches of Auckland’s Hauraki Gulf.

This was New Zealand’s best kept military secret, a mass destruction alternative to atomic weapons: Project Seal, the top-secret plan to build a tsunami bomb.

Today Shakespear Bay, north of Auckland, is a popular weekend spot for windsurfers, paddle boarders and visitors to the resident population of peacocks, but during the last years of World War Two the tranquil waters trembled with the concussion of almost 4000 test explosions.

Project Seal was a highly classified experiment to test the feasibility of destroying coastal defences, even cities, by producing a huge artificial tidal surge, a tsunami.

The idea was conceived by an American naval officer, Commander E A Gibson, after he observed that blasting operations to remove submerged coral reefs around Pacific islands sometimes produced an unexpectedly large wave.

He communicated his idea to the New Zealand Chief of General Staff, General Sir Edward Puttick, who took the concept to the New Zealand War Cabinet.

Tests off Noumea

Agreement was reached for a combined group of Americans and New Zealanders to conduct preliminary tests in New Caledonia. This was done off the coast of Noumea in February 1944.

Included in the group was acting New Zealand director of scientific developments, Auckland University, Professor T D Leech, the prominent local scientist who would later lead the research in New Zealand.

A report made to the US Pacific commander Admiral Halsey after the preliminary tests was so encouraging that he asked New Zealand to undertake further investigations in our waters.

Although couched in military officialese, Halsey’s memorandum to the New Zealand chief of staff beams at the possibility of swamping enemy settlements with a huge, man-made tidal wave. He writes:

"The results of these experiments, in my opinion, show that inundation in amphibious warfare has definite and far-reaching possibilities as an offensive weapon.

"It would be very desirable to have further developments carried out to establish a practicable method and procedure which could be used in offensive warfare.

"I would be grateful if this development could be continued to completion by New Zealand officers. All practicable assistance of facilities and personnel in this command will be at your disposal."

On May 5, 1944, the New Zealand War Cabinet took up the request and established an Array Research Unit under Professor Leech to conduct top-secret tests for a possible new bomb.

Around 150 people were assigned to the unit, which would use a fortress site on the Whangaparaoa Peninsula, just a short drive from Auckland.

Most of the work would be done by New Zealand engineers, but explosives and ordinance were provided by the US Navy.

Specialised equipment

A large amount of specialised equipment needed to be developed for the project, including remote-wave recording devices, radio-controlled firing mechanisms and specialised marine explosives.

During the experiments a number of British and American scientists interested in triggering deep-sea explosions were invited to observe the work as it progressed.

The Seal project commenced operations on June 6 ,1944, and continued until it was eventually closed down on January 8, 1945.

During that time about 3700 experimental explosions were carried out, with charges ranging from just a few grams to almost 300kg. TNT was the explosive of choice but sometimes nitro-starch or old-fashioned gelignite was used.

Initially, the research was conducted under a false assumption. British studies on deep-sea charges had suggested that the gas bubble from an underwater explosion would work best to produce "an offensive inundation" when the bomb was very deep.

This was proved wrong after the Project Seal tests showed that the best waves would be produced when the charge was set off close to the surface.

Project Seal also proved that single explosions would not generate a wave large enough to cause surf, let alone inundate and destroy enemy coastal defences.

Detonated in unison

To achieve efficient wave production with sufficient destructive force a number of charges had to be detonated in unison.

The boffins in the Hauraki Gulf determined that a line or array of massive charges totalling as much as two million kilograms, split up into 10 or so equal parts, detonated around 8km from shore, would produce a wave of 10-12m in height.

One problem that the programme discovered was that the depth at which the explosive was placed was critical: even a small deviation from optimum would rob the wave of energy and the tsunami would be a ripple rather than a roar.

Initially, the tsunami bomb was seen as having the same offensive potential as the atom bomb, which was still being secretly developed in the United States.

However, at the beginning of 1945 the Allies appeared to be winning the war in the Pacific and the operational priority of the Seal project was reduced.

When the project was closed down in early 1945 the experimental programme was incomplete and the full military potential of the weapon had yet to be realised.

The tests were considered largely successful, however, and in 1947 Professor Leech was invited by the US Assistant Secretary for the Navy to help with the analysis of data from the US nuclear tests at Bikini Atoll.

As late as the 1950s, postgraduate engineering students at Auckland University College were still working on the final summary on the 1940s experiments.

When it was completed, the report called The Generation of Wave Systems tabulated and analysed the statistical and scientific data from Project Seal and it remains today an interesting handbook of how to make waves.

In recent years, Project Seal has attracted the attention of an organisation usually associated with UFO research.

Huge deception

James Carrion from MUFON, the Mutual UFO Network group, has suggested that the project may have been a huge deception intended to deceive the Soviet Union into thinking that the United States had something even bigger in its arsenal than the atomic bomb.

He suggests it could have been used to unmask spies or distract the Soviets into wasting time chasing a frivolous or nonexistent programme.

Whatever the truth about Project Seal, it was one of the most top-secret missions ever conducted in New Zealand territory, and had it been successful may have provided mankind with yet another method of mass destruction.

From the perspective of current New Zealand attitudes to nuclear weapons, it seems almost inconceivable that the country was ever involved in the development of a weapons system that was intended to deliver destruction on such a massive scale.

The secret Project Seal documents were recently declassified, but many are still undergoing a vetting process and they remain restricted, still secret in the vaults of the archive.

ABOUT THE AUTHOR: Ray Waru has been involved in the television and radio industries for more than 30 years. He joined TVNZ in 1977 and directed and produced such local favourites and Fair Go and Country Calendar. This is his first book.