At a time when the Dad's Army cast and story ideas seemed to be running out of steam, the youngest cast member, Ian Lavender, was given a chance to really shine in this episode, and he didn't pass it up.
Captain Mainwaring is predictably disgusted when his platoon is roped in to play Nazi soldiers in a wartime propaganda film and he refuses to dress in German uniform. The "stupid boy", Private Pike, on the other hand, really gets into character as a smartly-dressed Nazi officer, and hams it up to hilarious effect.
Lavender's performance in many ways carries this episode, as we get an opportunity to see him step outside of the soppy adolescent Private Pike role he had perfected over the years, and display his wider natural comedy instincts. Without that, the episode wouldn't have been nearly as funny.