The underwater mine was located in Diélette, on the road leading to the EDF power plant. It was industrially exploited from 1877 before stopping definitively in 1962. When it was still in operation, it employed three hundred workers: miners, carters and blacksmiths. With the particularity of being dug under the sea in a rock extremely rich in iron, this mine was one of the most renowned in France. 

Before mining, Flamanville was famous for its granite quarries exploited since the 17th century.

Flamanville granite has been used in many buildings, including :

• The harbor of Cherbourg,
• The Obelisk needle in the Cherbourg town hall square,
• The Place de la Concorde and the Pont Neuf in Paris,
• The harbors of Querqueville, Le Homet and Ile Pelée.
• The church, the castle and several remarkable buildings in Flamanville and the surrounding area.

It was in the middle of the 19th century, when the need for granite diminished, that iron ore began to replace it. The first extractions took place at sea, near the outer jetty, from two wells 150 meters deep.

The mine was regularly dewatered to combat heavy seepage, but remained in operation until July 1962.