You're transported back to 1942. You, yourself are sitting in a cinema praying to God that you have personally not caused the deaths of hundreds of people. This isn't just a movie, it's a vital life or death message you need to heed.
These days we're familiar with spy stories. We've seen so many of those films that we know the tricks of the trade. To us now its hammer over the head approach in getting the message across seems oddly unsubtle but this was aimed at a 1942 population. The audience back then didn't have our experience, they didn't know what we now know. Without wanting to sound patronising, they did need educating, they needed to be told. The pitfalls of having loose lips had to be spelled out in black and white.
This isn't like a normal picture but neither is it a dry preachy lecture on how to behave. The filmmakers knew what they were doing: they knew how to engage with their audience, they knew they had to make this both informative, exciting and above all else, entertaining. It's very different to most wartime morale boosting movies, in fact as Churchill noted, it's quite depressing. That's what is so powerful about it - if you aren't careful, you, yes you might personally plunge the world into a living nightmare.
Besides being a genuinely entertaining piece of cinema, it's a genuinely important piece of history, an actual part of the war effort which we can now experience for ourselves.
