Helgoland | The Red Keep

After the Germans exchanged Helgoland with the British against Zanzibar in 1890, they turned it into a fortress island with a 13 km subterranean tunnel system.

On May 11th 1945, Helgoland came back under the control of British troops and soon became a bombing range.

On April 18th 1947, the Royal Navy detonated 6,700 tonnes of explosives during operation “Big Bang” creating one of the biggest single non-nuclear detonations in history.