US, Kiwis Tested Tsunami Bomb in WWII

'Tsunami bomb' tested off New Zealand coast

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.
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Mr Waru said the initial testing was positive but the project was eventually shelved in early 1945, though New Zealand authorities continued to produce reports on the experiments into the 1950s. Experts concluded that single explosions were not powerful enough and a successful tsunami bomb would require about 2 million kilograms of explosive arrayed in a line about five miles from shore.

So they would have needed  about 2 kilotons of explosive to produce a wave big enough to swamp a city, carefully laid, and detonated in a particular pattern?  Sounds a lot easier to take a fraction of that much explosive and drop it by air.

The Hiroshima bomb was 16 kilotons yield, centered in one small area.