Season 1 begins in the Autumn of 1942 with two storylines running parallel on land and at sea: the submarine warfare is becoming increasingly brutal and the Resistance begins to gain influence in La Rochelle.

U-612 with their new commander Klaus Hoffmann is ready for its maiden voyage and the crew has to cope with the cramped and claustrophobic conditions under water, as they are physically and mentally pushed to their limits. Meanwhile, at the port of La Rochelle, the world of Simone Strasser spirals out of control as she is engulfed in a dangerous liaison and forbidden love, torn between her loyalty for Germany and the Resistance.