Went the Day Well? is one of the British war movies made during WWII that were meant to strengthen morale and inspire steadfastness. The little English village of Bromley End welcomes a large number of Royal Engineers who are to work on a secret project. However, the Royal Engineers in reality are English-speaking German soldiers in British uniforms, parachuted into England to set up a counter radar apparatus which will disrupt England's radar network.
Gradually the villagers begin to suspect things aren't right, and then realize what they're dealing with. The Germans cordon off the village and show their true, ruthless nature. The villagers need to break through the cordon to alert authorities and get help. They also decide they must take action themselves to stop the Germans. This is complicated because the village houses a traitor. The climax is the Battle of Bromley End, with British Home Guard troops arriving while the Germans, attacking the manor house where they must set up their equipment, are held off by the brave men and women of the village.
You'll recognize some fine actors: Leslie Banks, David Farrar, Thora Hird, Basil Sydney, Mervyn Johns among others. The film is a well-constructed and effective bit of wartime home-front propaganda.