Calm at Sea takes place in a French occupation camp in 1941. The movie opens with the prisoners in the camp holding a race, while the men and women (who are separated) are flirting between the wires. No sense of danger seems imminent. Simultaneously outside, in Nantes, 3 members of the communist party take it upon themselves to shoot and kill a Nazi officer. This leads to the Nazi occupiers (and French collaborators) to reciprocally kill50 hostages for the act.
That more or less sums up the entire movie, and nothing happens to surprise one way or another. There are scenes of the French and Germans trying to avoid the outcome, some trying harder than others. We see the hostages rounded up in the camps, knowing what's coming, but doing nothing about it. And we march inexorably towards the climax of the movie.
Not to say there isn't a story to be told here, but this wasn't it. It felt stilted, disjointed, and without any real power. It wants to show the strength and resolve of the men, but fails in that regard.