This might have been just another wartime B film by a minor director about the resistance in Europe. But there is a touch of class, which may be evidence of its producers, Michael Powell and Emeric Pressburger. They brought in a superior crew, including cinematographer Erwin Hiller who shot on location, with East Anglia standing in for Netherlands.
There is a sensitivity to history, mythology and national identity which is typical of Powell and Pressburger. Ralph Richardson plays a Dutch shipbuilder who draws inspiration from his country's resistance to the Spanish piratical 'silver fleet' in 1628. He fronts up as a Nazi collaborator while secretly sabotaging the submarines built in his shipyard.
So he is despised by his countrymen, and doubted by his wife (Googie Withers). Richardson gives his standard performance of the war years, energetic, puckish and a bit mysterious. Esmond Knight contributes a caricature of a gestapo officer, cartoonishly grotesque, uncultured and sadistic. Even his own colleagues laugh at him.
While the Nazis are unrealistically ineffectual, there is some fascinating dialogue which touches on fascist assumptions of national superiority. An uncredited Pressburger co-wrote the script which offers a lyrical reflection on patriotic sacrifice. It's propaganda, and sometimes sentimental, but there is a thread of quality woven all the way through.