Obvious question: have they actually used it to cause any tsunamis to their enemies (or allies/friends who have strayed from total obedience to the orders of the masters)?

After they got nuclear bombs, they obviously could apply it to their "tsunami bomb" discovery while eliminating the need for huge amounts of conventional bomb material to initiate the tsunami.

'Tsunami bomb' tested off New Zealand coast
The United States and New Zealand conducted secret tests of a "tsunami bomb" designed to destroy coastal cities by using underwater blasts to trigger massive tidal waves.
By Jonathan Pearlman, Sydney, 2:50PM GMT 01 Jan 2013
"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."

Now, I also wonder if this may have any connection to the recent news of an island named "Sandy" being found to "not exist" by Australian scientists.  That "phantom island", near New Caledonia, New Zealand, existed on many maps for over a century, but upon this new discovery, it was promptly removed from all maps, including GoogleMaps.  http://www.cntraveler.com/daily-traveler/2012/12/sandy-island-new-caledonia-maphead-ken-jennings

I first read about the "non-existent" island Sandy in the article on Sandy Hood school shooting that Mitchel Cohen sent out, thanks Mitchel.