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Turtle Power Turtle Power

As Korea, sink an Ironclad with a Turtle Ship.

Taken from the Teenage Mutant Ninja Turtles film franchise.
This is a difficult achievement in 'normal' play as the Ironclad is only available for a short time and requires the player to have both Iron and Coal, therefore the AI doesn't build many Ironclads. Also, the achievement is not available in multi player mode. One recommended 'shortcut' is to build an Ironclad yourself and 'gift' it to a City State and then declare war on that City State.