The British army used 4000 tons of surplus WWII explosives to destroy an entire island!

In April 1947, British Army decided to destroy the North Sea Island, Heligoland.

They laced the island with about 4000 tons of leftover WWII ammunition. They then detonated the various explosives at once.
The island amazingly survived but it's many fortifications were destroyed. Despite the fact that they failed to get rid of the entire island, the British did secure a world record.

In the Guinness Book of World Records, this explosion is listed as the "largest single explosive detonation." The energy released was equal to 3.2 kilotons of TNT.