On the 29th of May 1937, off the coast of the Spanish island Ibiza, Soviet pilots flying bombers for the Spanish government spotted a target identified as a nationalist battle cruiser.
Only after hitting it and killing or wounding around 100 sailors did they discover their mistake.
It was a noncombatant German warship on patrol, the Deutschland.
Hitler was furious and decided to take revenge on the republican city of Almeria.
At dawn on May the 31st, just over four months after its construction began, Almeria's public air raid shelter, only one-quarter built, was called into action.
German warships moored along the coast opened fire on the city.
People started pouring into the tunnels, desperately trying to seek refuge from the hell that was unfolding above ground.
Hundreds of heavy naval shells rained down on Almeria, destroying 200 buildings.
You've got to try to picture what it would have been like down in these claustrophobic spaces with thousands of people, men, women, children, the elderly, stifling conditions, just trying to escape the nightmare above their heads.
The only defense they had was nine meters of soil.
