The Tsunami Bomb Plot: WWII’s Secret Plan to Unleash Waves on Enemy Shores

In World War II, New Zealand’s top scientists hatched a daring idea: could an explosion trigger a tsunami to wash away enemy ships and bases? Between 1944 and 1945, a secret project—code-named “Tsunami Bomb”—aimed to answer that question. Under strict secrecy, teams tested charges along remote coasts. Yet, despite early promise, the plan never reached battle. Its story reveals a blend of innovation, risk, and ethics in wartime.

Origins of the Tsunami Bomb Idea

By 1943, Allied forces sought new ways to strike Japan’s coastline. Conventional bombs and naval attacks faced stiff defense. At the same time, reports of underwater explosions showed that large charges could create local tidal waves. New Zealand’s Applied Physics Laboratory proposed using this effect as a weapon.

Dr. Thomas Leach, a leading engineer, led experiments at Whangaparaoa Peninsula near Auckland. Under dark skies and guarded by soldiers, teams laid explosive devices underwater. Their goal was to blow enough of a hole in the seabed to create a wave strong enough to damage ports or shorelines. Records at the New Zealand History archive detail early tests where small charges produced minor surges.

The military brass approved further trials. By mid-1944, scientists scaled up. Explosives went from a few hundred pounds to over two tons. They moved operations to remote Pacific atolls, including Pendennis Island. Secrecy was vital; not even most naval officers knew of the plan.

How the Plan Worked

The Tsunami Bomb scheme relied on timing, depth, and charge size. Scientists placed barrels of TNT in shallow water at low tide. As the tide rose, charges sank to the right depth. Synchronized detonation would then push large volumes of water, forming a wave that rolled toward shore.

In late 1944, tests off Tairua Heads produced waves nearly ten feet high. Observers on nearby boats recorded wave speed and height. A report in the Smithsonian Magazine explains that the wave energy spread quickly, but controlling its direction proved tricky. The Pacific tides and wind could disperse the wave, reducing its power before landfall.

Engineers believed five massive charges, spaced in a line, could strike a port town. They calculated that a combined wave might reach sixteen feet, enough to swamp docks, sink small ships, and flood coastal defenses. However, tests also revealed dangers: unburned debris and unpredictable currents could harm friendly vessels. Moreover, building and delivering huge explosives under war conditions was risky.

Why the Project Ended

By early 1945, tide tables and naval intelligence still hoped for a usable wave weapon. Yet a series of problems emerged:

1. Unpredictable Wave Direction: Wind and currents often sent waves off course. A bomb meant for one cove could flood another beach far away.

2. Logistics and Risk: Transporting tons of TNT to remote atolls exposed ships to enemy attack. Losing a supply ship would be disastrous.

3. Ethical and Strategic Concerns: High command worried about civilian casualties and long-term damage to coastal towns. A tsunami does not discriminate between military targets and noncombatants.

By March 1945, Japan’s defenses crumbled under conventional bombing. The urgency for a Tsunami Bomb faded. In April, the project was quietly canceled. Many files were sealed for decades and only declassified in the 1990s. Today, little remains but ship logs, lab notes, and a few photos in the Australian War Memorial collection.

Legacy and Real-World Impact

Though never used in combat, the Tsunami Bomb project left a lasting imprint. It taught engineers about the power of underwater explosions and wave physics. Research on wave generation influenced postwar studies in civil engineering and tsunami readiness.

In 1956, Dr. Leach published papers on underwater blast effects, guiding coastal defense and marine construction. His work helped design breakwaters that could withstand seismic waves. Modern tsunami warning systems also borrowed insights from those early notes on wave propagation.

Ethically, the Tsunami Bomb remains a cautionary tale. International law now classifies “environmental modification” for weapon use as illegal. The 1977 Environmental Modification Convention (ENMOD) bans deliberate manipulation of natural forces. While warfare has advanced, the experiment shows how wartime desperation can push science to dangerous edges.

Reflections on the Tsunami Bomb

The Tsunami Bomb plan straddles innovation and moral conflict. It shows how necessity can drive new science, yet also risks uncontrollable outcomes. If the project had continued, a single miscalculation could have led to massive civilian loss. In the end, conventional strategy won the day—and perhaps spared many lives.