[citation needed] The film tells the story of the Home Guard platoon's formation and their subsequent endeavours at a training exercise.

One morning, George Mainwaring, the manager of the Walmington-on-Sea branch of Martins Bank, and his chief clerk, Arthur Wilson, listen to Anthony Eden making a radio broadcast about forming the Local Defence Volunteers (LDV).

Characteristically, Mainwaring takes charge and after commandeering the local church hall he registers the assembled volunteers, with weapons being inspected.

The local platoon is eventually formed with Mainwaring in command as captain, Wilson as his sergeant and Jack Jones as the lance-corporal, plus Frazer, Godfrey, Pike and Walker as privates.

The chaos includes an anti-aircraft rocket launcher blowing up a farmer's barn and a one-man tank made from a cast iron bathtub rolling into the river with Private Joe Walker still inside.

After a night sleeping without tents the platoon, bar Wilson, oversleep and miss breakfast despite being detailed to hold a pontoon bridge during the day's exercise.

The bridge has been sabotaged by the Royal Marines and the results are comically chaotic, with Jones atop on a drifting white horse.

While the platoon are walking back to Walmington, a Luftwaffe reconnaissance aircraft is shot down and its three-man crew parachutes to safety.

The weather has changed for the worse and it is unlikely that Hitler will ever invade, although that does not stop the group lying down and listening when they start to suspect they have detected a Nazi attempt to tunnel into Britain.

The audience saw the Germans preparing across the Channel, rather than them simply being an unseen threat, and the events of the platoon's formation were revised in various ways for the big screen treatment.