Captain Mainwaring and his men create comedy mayhem when they go on manoeuvres with other military companies under the eye of a real Major-General. The result is disaster after disaster. After the shambles of manoeuvres, the Walmington-On-Sea defenders return home just as a German scout plane crashes near their town. It's crew captures the Church Hall and holds the Vicar and Major as hostages.

The Major-General sends for the Army, the Army sends for the Navy, the Navy sends for the Marines, the Marines call in the police, and the police call the fire brigade. While this is going on, the irrepressible irregulars of Dad's Army hilariously demonstrate that they really can do the job they were organised for...