The Next of Kin (1942)

This isn't so much an action film, as a series of scenarios that convey a message to the watching public that "careless talk costs lives". It started out life as a training film and you can tell by the rather clunky editing that director Thorold Dickinson was thinking on his feet as this project aimed at the military grew into a very important, and effective, counter-espionage tool. It's got quite a formidable cast of serving (or reservist) soldiers including Mervyn Johns, Jack Hawkins, Stephen Murray, Basil Sydney as well as Torin Thatcher in his typical role as the baddie; and the narrative weaves threads that cleverly expose just how easily the enemy got hold of information and capitalised on it. It uses actuality from time to time, and has a strange sort of excitement especially as the climaxes to each thread are not always favourable to the British which also lends it a considerable authenticity. There is a bit of wartime black humour to enjoy too, and though a curious film to watch, it has an unique plausibility which I found interesting, and to an extent, quite enjoyable.